Syllacon NOTES

Syllacon NOTES

SINGAPORE-CAMBRIDGE GCE O-LEVEL

PHYSICS OUTLINE

SYLLABUS 5059

UPDATED 20 JAN 2014

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2 ‘Consylladated’ by Lim Ting Jie

Overview

Themes Chapters Count

I. Measurement 1 1

II. Newtonian Mechanics 2-7 6

III. Thermal Physics 8-11 4

IV. Waves 12-15 4

V. Electricity & Magnetism 16-22 7

1. Physical Quantities, Units and Measurement ............................................................................ 12

2. Kinematics ................................................................................................................................ 17

3. Dynamics .................................................................................................................................. 20

4. Mass, Weight and Density......................................................................................................... 23

5. Turning Effect of Forces ............................................................................................................ 25

6. Pressure ................................................................................................................................... 27

7. Energy, Work and Power .......................................................................................................... 29

8. Kinetic Model of Matter ............................................................................................................. 32

9. Transfer of Thermal Energy ...................................................................................................... 34

10. Temperature ........................................................................................................................... 36

11. Thermal Properties of Matter ................................................................................................... 37

12. General Wave Properties ........................................................................................................ 41

13. Light ........................................................................................................................................ 44

14. Electromagnetic Spectrum ...................................................................................................... 49

15. Sound ..................................................................................................................................... 51

16. Static Electricity ....................................................................................................................... 54

17. Current of Electricity ................................................................................................................ 58

18. D.C. Circuits ............................................................................................................................ 63

19. Practical Electricity .................................................................................................................. 65

20. Magnetism .............................................................................................................................. 69

21. Electromagnetism ................................................................................................................... 71

22. Electromagnetic Induction ....................................................................................................... 77

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Contents

1. Physical Quantities, Units and Measurement ....................................................................... 12

(a) show understanding that all physical quantities consist of a numerical magnitude and a unit12

(b) recall the following base quantities and their units: mass (kg), length (m), time (s), current (A),

temperature (K), amount of substance (mol) ............................................................................. 12

(c) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of

the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G) ........... 12

(d) show an understanding of the orders of magnitude of the sizes of common objects ranging

from a typical atom to the Earth ................................................................................................. 12

(e) state what is meant by scalar and vector quantities and give common examples of each .... 13

(f) add two vectors to determine a resultant by a graphical method ........................................... 13

(g) describe how to measure a variety of lengths with appropriate accuracy by means of tapes,

rules, micrometers and calipers, using a vernier scale as necessary ......................................... 14

(h) describe how to measure a short interval of time including the period of a simple pendulum

with appropriate accuracy using stopwatches or appropriate instruments.................................. 15

2. Kinematics ............................................................................................................................... 17

(a) state what is meant by speed and velocity ........................................................................... 17

(b) calculate average speed using distance travelled / time taken ............................................. 17

(c) state what is meant by uniform acceleration and calculate the value of an acceleration using

change in velocity / time taken ................................................................................................... 17

(d) interpret given examples of non-uniform acceleration .......................................................... 18

(e) plot and interpret a displacement-time graph and a velocity-time graph ............................... 18

(f) deduce from the shape of a displacement-time graph when a body is: (i) at rest (ii) moving

with uniform velocity (iii) moving with non-uniform velocity ........................................................ 18

(g) deduce from the shape of a velocity-time graph when a body is: (i) at rest (ii) moving with

uniform velocity (iii) moving with uniform acceleration (iv) moving with non-uniform acceleration

.................................................................................................................................................. 18

(h) calculate the area under a velocity-time graph to determine the displacement travelled for

motion with uniform velocity or uniform acceleration .................................................................. 19

(i) state that the acceleration of free fall for a body near to the Earth is constant and is

approximately 10 m/s2 ............................................................................................................... 19

(j) describe the motion of bodies with constant weight falling with or without air resistance,

including reference to terminal velocity ...................................................................................... 19

3. Dynamics ................................................................................................................................. 20

(a) apply Newton's Laws to: (i) describe the effect of balanced and unbalanced forces on a body

(ii) describe the ways in which a force may change the motion of a body (iii) identify action-

reaction pairs acting on two interacting bodies (stating of Newton's Laws is not required) ......... 20

(b) identify forces acting on an object and draw free body diagram(s) representing the forces

acting on the object (for cases involving forces acting in at most 2 dimensions) ........................ 21

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(c) solve problems for a static point mass under the action of 3 forces for 2-dimensional cases (a

graphical method would suffice) ................................................................................................ 21

(d) recall and apply the relationship resultant force = mass × acceleration to new situations or to

solve related problems .............................................................................................................. 22

(e) explain the effects of friction on the motion of a body ........................................................... 22

4. Mass, Weight and Density ...................................................................................................... 23

(a) state that mass is a measure of the amount of substance in a body (b) state that mass of a

body resists a change in the state of rest or motion of the body (inertia).................................... 23

(c) state that a gravitational field is a region in which a mass experiences a force due to

gravitational attraction ............................................................................................................... 23

(d) define gravitational field strength, g, as gravitational force per unit mass ............................. 23

(e) recall and apply the relationship weight = mass × gravitational field strength to new situations

or to solve related problems ...................................................................................................... 23

(f) distinguish between mass and weight ................................................................................... 24

(g) recall and apply the relationship density = mass / volume to new situations or to solve related

problems ................................................................................................................................... 24

5. Turning Effect of Forces ......................................................................................................... 25

(a) describe the moment of a force in terms of its turning effect and relate this to everyday

examples (b) recall and apply the relationship moment of a force (or torque) = force ×

perpendicular distance from the pivot to new situations or to solve related problems ................ 25

(c) state the principle of moments for a body in equilibrium (d) apply the principle of moments to

new situations or to solve related problems ............................................................................... 25

(e) show understanding that the weight of a body may be taken as acting at a single point known

as its centre of gravity................................................................................................................ 25

(f) describe qualitatively the effect of the position of the centre of gravity on the stability of objects

.................................................................................................................................................. 26

6. Pressure .................................................................................................................................. 27

(a) define the term pressure in terms of force and area (b) recall and apply the relationship

pressure = force / area to new situations or to solve related problems....................................... 27

(c) describe and explain the transmission of pressure in hydraulic systems with particular

reference to the hydraulic press ................................................................................................ 27

(d) recall and apply the relationship pressure due to a liquid column = height of column × density

of the liquid × gravitational field strength to new situations or to solve related problems ............ 28

(e) describe how the height of a liquid column may be used to measure the atmospheric

pressure .................................................................................................................................... 28

(f) describe the use of a manometer in the measurement of pressure difference ....................... 28

7. Energy, Work and Power ........................................................................................................ 29

(a) show understanding that kinetic energy, potential energy (chemical, gravitational, elastic),

light energy, thermal energy, electrical energy and nuclear energy are examples of different

forms of energy ......................................................................................................................... 29

(b) state the principle of the conservation of energy and apply the principle to new situations or to


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(c) calculate the efficiency of an energy conversion using the formula efficiency = energy

converted to useful output / total energy input ........................................................................... 29

(d) state that kinetic energy Ek = ½ mv2 and gravitational potential energy Ep = mgh (for potential

energy changes near the Earth’s surface) (e) apply the relationships for kinetic energy and

potential energy to new situations or to solve related problems ................................................. 30

(f) recall and apply the relationship work done = force × distance moved in the direction of the

force to new situations or to solve related problems .................................................................. 30

(g) recall and apply the relationship power = work done / time taken to new situations or to solve

related problems ........................................................................................................................ 30

8. Kinetic Model of Matter ........................................................................................................... 32

(a) compare the properties of solids, liquids and gases ............................................................. 32

(b) describe qualitatively the molecular structure of solids, liquids and gases, relating their

properties to the forces and distances between molecules and to the motion of the molecules . 32

(c) infer from Brownian motion experiment the evidence for the movement of molecules .......... 32

(d) describe the relationship between the motion of molecules and temperature ....................... 33

(e) explain the pressure of a gas in terms of the motion of its molecules ................................... 33

(f) recall and explain the following relationships using the kinetic model (stating of the

corresponding gas laws is not required): (i) a change in pressure of a fixed mass of gas at

constant volume is caused by a change in temperature of the gas (ii) a change in volume

occupied by a fixed mass of gas at constant pressure is caused by a change in temperature of

the gas (iii) a change in pressure of a fixed mass of gas at constant temperature is caused by a

change in volume of the gas ...................................................................................................... 33

(g) use the relationships in (f) in related situations and to solve problems (a qualitative treatment

would suffice) ............................................................................................................................ 33

9. Transfer of Thermal Energy ................................................................................................... 34

(a) show understanding that thermal energy is transferred from a region of higher temperature to

a region of lower temperature .................................................................................................... 34

(b) describe, in molecular terms, how energy transfer occurs in solids ...................................... 34

(c) describe, in terms of density changes, convection in fluids ................................................... 34

(d) explain that energy transfer of a body by radiation does not require a material medium and

the rate of energy transfer is affected by: (i) colour and texture of the surface (ii) surface

temperature (iii) surface area ..................................................................................................... 34

(e) apply the concept of thermal energy transfer to everyday applications ................................. 35

10. Temperature .......................................................................................................................... 36

(a) explain how a physical property which varies with temperature, such as volume of liquid

column, resistance of metal wire and electromotive force (e.m.f.) produced by junctions formed

with wires of two different metals, may be used to define temperature scales ........................... 36

(b) describe the process of calibration of a liquid-in-glass thermometer, including the need for

fixed points such as the ice point and steam point ..................................................................... 36

11. Thermal Properties of Matter ............................................................................................... 37

(a) describe a rise in temperature of a body in terms of an increase in its internal energy (random

thermal energy) ......................................................................................................................... 37

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(b) define the terms heat capacity and specific heat capacity .................................................... 37

(c) recall and apply the relationship thermal energy = mass × specific heat capacity × change in

temperature to new situations or to solve related problems ....................................................... 37

(d) describe melting/solidification and boiling/condensation as processes of energy transfer

without a change in temperature ............................................................................................... 38

(e) explain the difference between boiling and evaporation ....................................................... 38

(f) define the terms latent heat and specific latent heat .............................................................. 38

(g) recall and apply the relationship thermal energy = mass × specific latent heat to new

situations or to solve related problems ...................................................................................... 38

(h) explain latent heat in terms of molecular behaviour .............................................................. 39

(i) sketch and interpret a cooling curve ...................................................................................... 39

12. General Wave Properties ...................................................................................................... 41

(a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs and

by waves in a ripple tank ........................................................................................................... 41

(b) show understanding that waves transfer energy without transferring matter......................... 42

(c) define speed, frequency, wavelength, period and amplitude ................................................ 42

(d) state what is meant by the term wavefront ........................................................................... 43

(e) recall and apply the relationship velocity = frequency × wavelength to new situations or to


(f) compare transverse and longitudinal waves and give suitable examples of each .................. 43

13. Light ....................................................................................................................................... 44

(a) recall and use the terms for reflection, including normal, angle of incidence and angle of

reflection.................................................................................................................................... 44

(b) state that, for reflection, the angle of incidence is equal to the angle of reflection and use this

principle in constructions, measurements and calculations ........................................................ 44

(c) recall and use the terms for refraction, including normal, angle of incidence and angle of

refraction ................................................................................................................................... 45

(d) recall and apply the relationship sin i / sin r = constant to new situations or to solve related

problems (e) define refractive index of a medium in terms of the ratio of speed of light in vacuum

and in the medium ..................................................................................................................... 45

(f) explain the terms critical angle and total internal reflection .................................................... 46

(g) identify the main ideas in total internal reflection and apply them to the use of optical fibres in

telecommunication and state the advantages of their use ......................................................... 46

(h) describe the action of a thin lens (both converging and diverging) on a beam of light .......... 47

(i) define the term focal length for a converging lens ................................................................. 47

(j) draw ray diagrams to illustrate the formation of real and virtual images of an object by a thin

converging lens ......................................................................................................................... 48

14. Electromagnetic Spectrum ................................................................................................... 49

(a) state that all electromagnetic waves are transverse waves that travel with the same speed in

vacuum and state the magnitude of this speed .......................................................................... 49

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(b) describe the main components of the electromagnetic spectrum (c) state examples of the use

of the following components: (i) radiowaves (e.g. radio and television communication) (ii)

microwaves (e.g. microwave oven and satellite television) (iii) infra-red (e.g. infra-red remote

controllers and intruder alarms) (iv) light (e.g. optical fibres for medical uses and

telecommunications) (v) ultra-violet (e.g. sunbeds and sterilisation) (vi) X-rays (e.g. radiological

and engineering applications) (vii) gamma rays (e.g. medical treatment)................................... 50

(d) describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and damage

to living cells and tissue ............................................................................................................. 50

15. Sound..................................................................................................................................... 51

(a) describe the production of sound by vibrating sources (b) describe the longitudinal nature of

sound waves in terms of the processes of compression and rarefaction ................................... 51

(c) explain that a medium is required in order to transmit sound waves and the speed of sound

differs in air, liquids and solids ................................................................................................... 51

(d) describe a direct method for the determination of the speed of sound in air and make the

necessary calculation ................................................................................................................ 51

(e) relate loudness of a sound wave to its amplitude and pitch to its frequency ......................... 52

(f) describe how the reflection of sound may produce an echo, and how this may be used for

measuring distances ................................................................................................................. 52

(g) define ultrasound and describe one use of ultrasound, e.g. quality control and pre-natal

scanning .................................................................................................................................... 52

16. Static Electricity .................................................................................................................... 54

(a) state that there are positive and negative charges and that charge is measured in coulombs

.................................................................................................................................................. 54

(b) state that unlike charges attract and like charges repel ........................................................ 54

(c) describe an electric field as a region in which an electric charge experiences a force (d) draw

the electric field of an isolated point charge and recall that the direction of the field lines gives the

direction of the force acting on a positive test charge ................................................................ 54

(e) draw the electric field pattern between two isolated point charges ....................................... 55

(f) show understanding that electrostatic charging by rubbing involves a transfer of electrons ... 55

(g) describe experiments to show electrostatic charging by induction ........................................ 56

(h) describe examples where electrostatic charging may be a potential hazard ......................... 56

(i) describe the use of electrostatic charging in a photocopier, and apply the use of electrostatic

charging to new situations ......................................................................................................... 57

17. Current of Electricity ............................................................................................................. 58

(a) state that current is a rate of flow of charge and that it is measured in amperes ................... 58

(b) distinguish between conventional current and electron flow ................................................. 58

(c) recall and apply the relationship charge = current × time to new situations or to solve related

problems ................................................................................................................................... 58

(d) define electromotive force (e.m.f.) as the work done by a source in driving unit charge around

a complete circuit ...................................................................................................................... 59

(e) calculate the total e.m.f. where several sources are arranged in series ................................ 59

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(f) state that the e.m.f. of a source and the potential difference (p.d.) across a circuit component

is measured in volts (g) define the p.d. across a component in a circuit as the work done to drive

unit charge through the component ........................................................................................... 59

(h) state the definition that resistance = p.d. / current (i) apply the relationship R = V/I to new

situations or to solve related problems ...................................................................................... 59

(j) describe an experiment to determine the resistance of a metallic conductor using a voltmeter

and an ammeter, and make the necessary calculations ............................................................ 60

(k) recall and apply the formulae for the effective resistance of a number of resistors in series

and in parallel to new situations or to solve related problems .................................................... 60

(l) recall and apply the relationship of the proportionality between resistance and the length and

cross-sectional area of a wire to new situations or to solve related problems ............................ 61

(m) state Ohm’s Law ................................................................................................................. 61

(n) describe the effect of temperature increase on the resistance of a metallic conductor ......... 61

(o) sketch and interpret the I/V characteristic graphs for a metallic conductor at constant

temperature, for a filament lamp and for a semiconductor diode ............................................... 62

18. D.C. Circuits .......................................................................................................................... 63

(a) draw circuit diagrams with power sources (cell, battery, d.c. supply or a.c. supply), switches,

lamps, resistors (fixed and variable), variable potential divider (potentiometer), fuses, ammeters

and voltmeters, bells, light-dependent resistors, thermistors and light-emitting diodes .............. 63

(b) state that the current at every point in a series circuit is the same and apply the principle to

new situations or to solve related problems (c) state that the sum of the potential differences in a

series circuit is equal to the potential difference across the whole circuit and apply the principle

to new situations or to solve related problems (d) state that the current from the source is the

sum of the currents in the separate branches of a parallel circuit and apply the principle to new

situations or to solve related problems (e) state that the potential difference across the separate

branches of a parallel circuit is the same and apply the principle to new situations or to solve

related problems ........................................................................................................................ 64

(f) recall and apply the relevant relationships, including R = V/I and those for current, potential

differences and resistors in series and in parallel circuits, in calculations involving a whole circuit

.................................................................................................................................................. 64

(g) describe the action of a variable potential divider (potentiometer) ........................................ 64

(h) describe the action of thermistors and light-dependent resistors and explain their use as input

transducers in potential dividers (i) solve simple circuit problems involving thermistors and light-

dependent resistors ................................................................................................................... 64

19. Practical Electricity ............................................................................................................... 65

(a) describe the use of the heating effect of electricity in appliances such as electric kettles,

ovens and heaters ..................................................................................................................... 65

(b) recall and apply the relationships P = VI and E = VIt to new situations or to solve related

problems ................................................................................................................................... 65

(c) calculate the cost of using electrical appliances where the energy unit is the kW h .............. 65

(d) compare the use of non-renewable and renewable energy sources such as fossil fuels,

nuclear energy, solar energy, wind energy and hydroelectric generation to generate electricity in

terms of energy conversion efficiency, cost per kW h produced and environmental impact ....... 66

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(e) state the hazards of using electricity in the following situations: (i) damaged insulation (ii)

overheating of cables (iii) damp conditions ................................................................................ 67

(f) explain the use of fuses and circuit breakers in electrical circuits and of fuse ratings ............ 67

(g) explain the need for earthing metal cases and for double insulation ..................................... 67

(h) state the meaning of the terms live, neutral and earth .......................................................... 67

(i) describe the wiring in a mains plug ........................................................................................ 68

(j) explain why switches, fuses, and circuit breakers are wired into the live conductor ............... 68

20. Magnetism ............................................................................................................................. 69

(a) state the properties of magnets ............................................................................................ 69

(b) describe induced magnetism ................................................................................................ 69

(c) describe electrical methods of magnetisation and demagnetisation ..................................... 69

(d) draw the magnetic field pattern around a bar magnet and between the poles of two bar

magnets (e) describe the plotting of magnetic field lines with a compass .................................. 70

(f) distinguish between the properties and uses of temporary magnets (e.g. iron) and permanent

magnets (e.g. steel) ................................................................................................................... 70

21. Electromagnetism ................................................................................................................. 71

(a) draw the pattern of the magnetic field due to currents in straight wires and in solenoids and

state the effect on the magnetic field of changing the magnitude and/or direction of the current 71

(b) describe the application of the magnetic effect of a current in a circuit breaker .................... 72

(c) describe experiments to show the force on a current-carrying conductor, and on a beam of

charged particles, in a magnetic field, including the effect of reversing (i) the current (ii) the

direction of the field ................................................................................................................... 73

(d) deduce the relative directions of force, field and current when any two of these quantities are

at right angles to each other using Fleming’s left-hand rule ....................................................... 74

(e) describe the field patterns between currents in parallel conductors and relate these to the

forces which exist between the conductors (excluding the Earth’s field) .................................... 74

(f) explain how a current-carrying coil in a magnetic field experiences a turning effect and that

the effect is increased by increasing (i) the number of turns on the coil (ii) the current .............. 75

(g) discuss how this turning effect is used in the action of an electric motor .............................. 75

(h) describe the action of a split-ring commutator in a two-pole, single-coil motor and the effect of

winding the coil on to a soft-iron cylinder ................................................................................... 76

22. Electromagnetic Induction ................................................................................................... 77

(a) deduce from Faraday’s experiments on electromagnetic induction or other appropriate

experiments: (i) that a changing magnetic field can induce an e.m.f. in a circuit (ii) that the

direction of the induced e.m.f. opposes the change producing it ................................................ 77

(iii) the factors affecting the magnitude of the induced e.m.f. ..................................................... 78

(b) describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip

rings (where needed) (c) sketch a graph of voltage output against time for a simple a.c.

generator ................................................................................................................................... 79

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(d) describe the use of a cathode-ray oscilloscope (c.r.o.) to display waveforms and to measure

potential differences and short intervals of time (detailed circuits, structure and operation of the

c.r.o. are not required) ............................................................................................................... 80

(e) interpret c.r.o. displays of waveforms, potential differences and time intervals to solve related

problems ................................................................................................................................... 81

(f) describe the structure and principle of operation of a simple iron-cored transformer as used

for voltage transformations ........................................................................................................ 82

(g) recall and apply the equations VP / VS = NP / NS and VPIP = VSIS to new situations or to solve

related problems (for an ideal transformer) ................................................................................ 82

(h) describe the energy loss in cables and deduce the advantages of high voltage transmission

.................................................................................................................................................. 82

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SECTION I: MEASUREMENT

Overview In order to gain a better understanding of the physical world, scientists use a process of investigation that follows a general cycle of observation, hypothesis, deduction, test and revision, sometimes referred to as the scientific method. Galileo Galilei, one of the earliest architects of this method, believed that the study of science had a strong logical basis that involved precise definitions of terms and physical quantities, and a mathematical structure to express relationships between these physical quantities. In this section, we study a set of base physical quantities and units that can be used to derive all other physical quantities. These precisely defined quantities and units, with accompanying order-of-ten prefixes (e.g. milli, centi and kilo) can then be used to describe the interactions between objects in systems that range from celestial objects in space to sub-atomic particles.

Extracted from PHYSICS GCE ORDINARY LEVEL (2014) Syllabus Document

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1. Physical Quantities, Units and Measurement

Content

• Physical quantities

• SI units

• Prefixes

• Scalars and vectors

• Measurement of length and time

Learning Outcomes

Candidates should be able to:

(a) show understanding that all physical quantities consist of a numerical magnitude and a

unit

Term Definition Constituents

Physical quantity Quantity that can be measured [no need to remember this definition]

• A numerical magnitude

• A unit

(b) recall the following base quantities and their units: mass (kg), length (m), time (s),

current (A), temperature (K), amount of substance (mol)

Term Base quantity (Derived quantities, e.g. area, are derived from base quantities, e.g. length)

Type Mass Length Time Current Temperature Amount of substance

SI unit kilograms metres seconds amperes Kelvin mole

Unit symbol kg m s A K mol

(c) use the following prefixes and their symbols to indicate decimal sub-multiples and

multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M),

giga (G)

Magnitude +ve sign prefix (symbol) −ve sign prefix (symbol) Examples (where 1 ≤ y < 10)

×10±1 deca- (da) deci- (d) • y kg = y ×103 g

• y cm = y ×10−2 m

• y cm2 = y ×10−4 m2

• y cm3 = y ×10−6 m3

• y m = y ×102 cm

• y m2 = y ×104 cm2

• y m3 = y ×106 cm3

×10±2 hexa- (h) centi- (c)

×10±3 kilo- (k) milli- (m)

×10±6 mega- (M) micro- (µ)

×10±9 giga- (G) nano- (n)

(d) show an understanding of the orders of magnitude of the sizes of common objects

ranging from a typical atom to the Earth

Object H atom Chopsticks length Football field length Mount Everest’s height Earth’s radius

Magnitude 110−15 m 210−1 m 1102 m 8.848103 m 6.378106 m

Note: There is no need to remember these magnitudes, an appreciation will do

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(e) state what is meant by scalar and vector quantities and give common examples of each

Term Definition

Scalar quantity Physical quantities that have magnitude only

Vector quantity Physical quantities that possess both magnitude and direction

Examples

Scalar Vector

Distance Displacement

Speed Velocity

Energy Force

Mass Weight

(f) add two vectors to determine a resultant by a graphical method

Determination of resultant force

Case

Case 1: Parallel vectors

Case 2: Non-parallel vectors

Case 2a: Same origin Case 2b: Tip-to-tail

Steps

Step 1: Calculate resultant force

Step 1: Write down the scale using 1 cm : ? N (scale must allow diagram drawn to be more than half of the space given in question)

Step 2: Draw the 2 forces with single arrows according to the scale

Step 3: Finish the parallelogram with dotted lines using set square

Step 4: Draw resultant force from the origin with a double arrow

Step 5: Measure length of resultant force


Step 1: Write down the scale using 1 cm : ? N (scale must allow diagram drawn to be more than half of the space given in question)

Step 2: Draw the 2 forces with single arrows according to the scale

Step 3: Draw resultant force from the start to end of the 2 forces with a double arrow

Step 4: Measure length of resultant force


Example

3N 5N Resultant force = 5N − 3N = 2N in the forward direction

Scale: 1 cm : 0.5 N Resultant force = 3.5 ÷ 0.5 = 7 N, acting 18o to the horizontal

Scale: 1 cm : 0.5 N Resultant force = 3.5 ÷ 0.5 = 7 N, acting 76o to the horizontal

5 N

3 N

7 N

40o 18o

20o

5 N

3 N

4.4 N 40o

20o 76o

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(g) describe how to measure a variety of lengths with appropriate accuracy by means of

tapes, rules, micrometers and calipers, using a vernier scale as necessary

# Instrument Precision Purpose Method of measurement Possible

error

1 Tape 10−1 cm To measure widths (e.g. long distances)

Position eye directly above the markings on the tape when making measurement to avoid parallax error

Parallax error

2 Metre rule 10−1 cm To measure depths (e.g. of ponds)

• Measure from a randomly chosen point instead of the ends to avoid zero error (from wear and tear)

• Substract the reading at the start of the object from the reading at the end of the object

Parallax error

3 Caliper 10−1 cm • To measure circular objects

• To measure cylinders

Circular objects

• Use jaws of the external calipers to grip the widest part of the circular object

• Distance between jaws is measured with a metre rule

Cylinders

• Invert the jaws to use the internal calipers

• Use jaws of the internal calipers to measure the inner diameter of the cylinder

• Distance between jaws is measured with a metre rule

Parallax error

4 Vernier caliper

10−2 cm • To measure the internal and external diameters of an object

• Consists of a main scale and a sliding vernier scale

• Grip the object using the correct pair of jaws

• Read the main scale directly opposite the zero mark on the vernier scale (e.g. 2.4 cm)

• Read the vernier mark that coincides with a marking on the main scale (e.g. +0.03 cm)

• Close the vernier caliper to check for zero error to be corrected (e.g. +0.02 cm)

• Calculate the final reading by adding the vernier reading and substracting the zero error [e.g. 2.4 + (+0.03) − (+0.02) = 2.41 cm]

Zero error

5 Micrometer screw gauge

10−3 cm To measure the external diameter of small precision (e.g. wires, ball bearings)

• Turn the thimble such that the object is gripped gently

• Turn the ratchet until it starts to click

• Read the main scale reading at the edge of the thimble (e.g. 6.5 mm)

• Read the thimble scale reading (reading 35 indicates 0.35 mm)

• Close the micrometer screw guage to check for zero error to be corrected (e.g. +0.02 mm)

• Calculate the final reading by adding the vernier reading and substracting the zero error [e.g. 6.5 + (+0.35) − (+0.02) = 6.65 cm]

Zero error

Note: This is mainly important for practical sessions

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(h) describe how to measure a short interval of time including the period of a simple

pendulum with appropriate accuracy using stopwatches or appropriate instruments

Term Meaning as for a pendulum

Oscillation Each complete to-and-fro motion of the pendulum bob

Period Time taken for one complete oscillation

Instrument Precision Method of measurement of

pendulum period Factors affecting period

of the pendulum Possible

error

Stopwatch 10−2 s • Measure the time taken for the pendulum to make 20 oscillations

• Find the period accurately by dividing the total time by 20

• Length of string affects the period

• Mass of bob does not affect the period

Human reaction time (about 0.3 to 0.5 s)

Note: This is mainly important for practical sessions

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SECTION II: NEWTONIAN MECHANICS

Overview Mechanics is the branch of physics that deals with the study of motion and its causes. Through a careful process of observation and experimentation, Galileo Galilei used experiments to overturn Aristotle’s ideas of the motion of objects, for example the flawed idea that heavy objects fall faster than lighter ones, which dominated physics for about 2,000 years. The greatest contribution to the development of mechanics is by one of the greatest physicists of all time, Isaac Newton. By extending Galileo’s methods and understanding of motion and gravitation, Newton developed the three laws of motion and his law of universal gravitation, and successfully applied them to both terrestrial and celestial systems to predict and explain phenomena. He showed that nature is governed by a few special rules or laws that can be expressed in mathematical formulae. Newton’s combination of logical experimentation and mathematical analysis shaped the way science has been done ever since. In this section, we begin by examining kinematics, which is a study of motion without regard for the cause. After which, we study the conditions required for an object to be accelerated and introduce the concept of forces through Newton’s Laws. Subsequently, concepts of moments and pressure are introduced as consequences of a force. Finally, this section rounds up by leading the discussion from force to work and energy, and the use of the principle of conservation of energy to explain interactions between bodies.


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2. Kinematics

Content

• Speed, velocity and acceleration

• Graphical analysis of motion

• Free-fall

• Effect of air resistance

Learning Outcomes


(a) state what is meant by speed and velocity

Term Definition

Average speed Total distance travelled per unit time

Velocity Change in displacement per unit time

(b) calculate average speed using distance travelled / time taken

Term Formula

Average speed DistanceAverage speed

Time taken=

(c) state what is meant by uniform acceleration and calculate the value of an acceleration

using change in velocity / time taken

Common legend

Key t a u v s

Term Time taken Acceleration Initial velocity Final velocity Displacement

Term Definition Formulae

Acceleration Change in velocity per unit time •

Change in velocityAcceleration

Time taken=

• v u

at

−=

Uniform acceleration Constant change in velocity per unit time N.A.

Related formulae to find acceleration

Given Formula to use

Time taken & Final velocity v u at= +

Time taken & Displacement 212

s ut at= +

Final velocity & Displacement 2 2 2v u as= +

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(d) interpret given examples of non-uniform acceleration

Non-uniform acceleration Uniform acceleration

Increasing acceleration Decreasing acceleration

Pushing on the pedal Releasing force on the pedal No change in force exerted on the pedal (e.g. pushing the pedal all the way)

(e) plot and interpret a displacement-time graph and a velocity-time graph

Differences Displacement-time graph Velocity-time graph

Label of y-axis Displacement / m Velocity / m s-1

Label of x-axis Time / s Time / s

Area below graph N.A. Total displacement / m

Gradient of graph Velocity / m s-1 Acceleration / m s-2

(f) deduce from the shape of a displacement-time graph when a body is: (i) at rest (ii)

moving with uniform velocity (iii) moving with non-uniform velocity

Displacement-time graph

Scenarios Displacement Gradient

At rest Zero displacement N.A.

Moving with uniform velocity Increasing displacement Constant gradient

Moving with non-uniform velocity Varying displacement Varying gradient

(g) deduce from the shape of a velocity-time graph when a body is: (i) at rest (ii) moving

with uniform velocity (iii) moving with uniform acceleration (iv) moving with non-uniform

acceleration

Velocity-time graph

Scenarios Velocity Gradient

At rest Zero velocity N.A.

Moving with uniform velocity Constant velocity Zero gradient

Moving with uniform acceleration Increasing velocity Constant gradient

Moving with non-uniform acceleration Varying velocity Varying gradient

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(h) calculate the area under a velocity-time graph to determine the displacement travelled

for motion with uniform velocity or uniform acceleration

Term Formulae

Displacement Displacement Area under velocity-time graph=

Area of square Velocity Time taken=

12

Area of triangle Velocity Time taken=

Term Formulae in symbols

Displacement ( )( )12

s v u t= +

Average velocity ( )12

Average velocity v u= +

(i) state that the acceleration of free fall for a body near to the Earth is constant and is

approximately 10 m/s2

Relationship between force and acceleration

• When a force is exerted on an object, the object will experience constant acceleration in the direction of the force if there is no other force acting against it (i.e. constant resultant force)

• Any free falling object near to the Earth will experience constant acceleration of approximately 10 m/s2 due to gravity as there is no air resistance acting against it

• Acceleration will only decrease when the object enters Earth as it will then experience air resistance

(j) describe the motion of bodies with constant weight falling with or without air resistance,

including reference to terminal velocity

Differences With air resistance Without air resistance

Description of motion of bodies with constant weight

▪ As an object falls in air, ▪ it increases its speed with an initial acceleration of 10ms-2 ▪ Air resistance opposing weight increases as speed

increases, ▪ causing resultant force and hence acceleration to decrease ▪ When air resistance is equal to the weight of the body, ▪ the forces balance out to zero resultant force causing zero

acceleration and the object travels at constant terminal velocity

▪ As an object falls in a vacuum,

▪ it increases its speed with an uniform acceleration of 10ms-2

▪ This is because there is no air resistance present,

▪ thus resultant force is constant

Graph of velocity against time

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3. Dynamics

Content

• Balanced and unbalanced forces

• Free-body diagram

• Friction

Learning Outcomes


(a) apply Newton's Laws to: (i) describe the effect of balanced and unbalanced forces on a

body (ii) describe the ways in which a force may change the motion of a body (iii) identify

action-reaction pairs acting on two interacting bodies (stating of Newton's Laws is not

required)

Scenarios Description Possible effects Condition

Balanced forces on a body

Resultant force is equal to 0 N

Object at rest Object initially at rest

Object travels at constant speed in a straight line

Object initally in motion

Unbalanced forces on a body

Resultant force is more than 0 N

Object accelerates • Object is initially at rest

• or Force in same direction as object’s motion

Object decelerates Force in opposite direction to object’s motion

Object changes direction Force acts at an angle to object’s motion

Illustrations of unbalanced forces

Object accelerates Object decelerates Object changes direction

Term Meaning Example Relationship

Action force

The force a body (body 1) exerts on another body (body 2)

Feet of a swimmer pushing against the swimming pool wall

• Forces always occur in pairs, each made up of a action force and a reaction force

▪ Action and reaction forces are equal in magnitude,

▪ act in opposite directions and ▪ on 2 different bodies

Reaction force

The subsequent force body 2 exerts on body 1 in reaction to the action force

Force that propels in swimmer forward in reaction

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(b) identify forces acting on an object and draw free body diagram(s) representing the

forces acting on the object (for cases involving forces acting in at most 2 dimensions)

Legend

Key Term Explanation

T Thrust N.A.

W Weight of object Due to gravity

F Force N.A.

+F Contact force Reaction force due to weight of object

*f Friction Between object and ground

R Air resistance Friction between object and air molecules

Air resistance applicable Object thrust upwards Object released high up

Without air resistance

With air resistance

Air resistance not applicable

Object on the ground Object pushed on the ground →

(c) solve problems for a static point mass under the action of 3 forces for 2-dimensional

cases (a graphical method would suffice)

References

Refer to Learning Outcome 1(f) on Page 13

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(d) recall and apply the relationship resultant force = mass × acceleration to new situations

or to solve related problems

Term Formula SI units Interpretation

Resultant force

• Resultant force Mass Acceleration=

• F ma=

F m a A resultant force of 2 N exerted on

a body of mass 0.5 kg causes the

body to accelerate at 4 m s-2 N kg m s-2

(e) explain the effects of friction on the motion of a body

Scenario Possible motions Explanation

Box rests on a flat horizontal floor

Box remains at rest • There is no frictional force acting on the box

• Contact force of the ground is equal to the weight of the box due to gravity

Box slides along a rough table

Decelerates and eventually stops

• Frictional force opposes the force of the motion

• Kinetic energy is converted to heat energy

Box rests on a slope Box remains at rest • Downward force of attraction acting on the box due to gravity is equal to the upward frictional force

• Resultant force is zero

Box accelerates down the slope

• Downward force of attraction acting on the box due to gravity is more than the upward frictional force

• Resultant force is more than zero

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4. Mass, Weight and Density

Content

• Mass and weight

• Gravitational field and field strength

• Density

Learning Outcomes


(a) state that mass is a measure of the amount of substance in a body (b) state that mass of

a body resists a change in the state of rest or motion of the body (inertia)

Term Definition

Mass Measure of the amount of substance in a body which resists a change in the state of rest or motion of the body

Inertia The resistance of a body with mass to start moving if it is stationary or stop moving if it is in motion in its first instance

(c) state that a gravitational field is a region in which a mass experiences a force due to

gravitational attraction

Term Definition

Gravitational field A region in which a mass experiences a force due to gravitational attraction

(d) define gravitational field strength, g, as gravitational force per unit mass

Term Definition

Gravitational field strength • Gravitational force acting per unit mass on an object

• The gravitational field strength on Earth is about 10 N kg-1

(e) recall and apply the relationship weight = mass × gravitational field strength to new

situations or to solve related problems

Term Definition Formula SI units Interpretation

Weight The force of attraction on an object due to gravity

• Weight

Mass Gravitational field strength=

• W mg=

• g on Earth is about 10 N kg-1

W m g A 2 kg mass has a weight of 20 N due to Earth’s gravitational pull of 10 N kg-1 kg N N kg-1

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(f) distinguish between mass and weight

Differences Mass Weight

Meaning Amount of matter in a body Due to pull of gravity on a body

Scalar or vector Scalar; has only magnitude Vector; has both magnitude and direction

Unit Measured in kg (kilograms) Measures in N (newtons)

Variations Constant regardless of gravitational field strength

Varies according to gravitational field strength

(g) recall and apply the relationship density = mass / volume to new situations or to solve

related problems


Density Mass per unit volume •

MassDensity

Volume=

• m

V =

m V An object with mass of 4 kg and volume of 2 m3 has a density of 2 kg m-3

kg m-3 kg m3

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5. Turning Effect of Forces

Content

• Moments

• Centre of gravity

• Stability

Learning Outcomes


(a) describe the moment of a force in terms of its turning effect and relate this to everyday

examples (b) recall and apply the relationship moment of a force (or torque) = force ×

perpendicular distance from the pivot to new situations or to solve related problems

Term Definition

Turning effect • The turning of an object about a pivot

• The greater the moment, the greater the object turns about the pivot


Moment of a force

The product of the force and the perpendicular distance between the line of action of the force and a pivot, and resulting in a turning effect

• Moment

Force Perpendicular distance=

• Moment F pd=

Moment F pd A force of 2 N acting with a perpendicular distance of 2 m produces a moment of 4 Nm

Nm N m

(c) state the principle of moments for a body in equilibrium (d) apply the principle of

moments to new situations or to solve related problems

Term Definition Formula

Principle of moments

When an object is in equilibrium, the sum of clockwise moments about a pivot is equal to sum of anticlockwise moments about the same pivot

Sum of clockwise moments Sum of anti-clockwise moments=

(e) show understanding that the weight of a body may be taken as acting at a single point

known as its centre of gravity

Term Definition Alternative definition

Centre of gravity of an object

Point of application of the resultant force on an object exerted by gravity for any orientation of the object

Point through which the whole weight of an object appears to act for any orientation of the object

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(f) describe qualitatively the effect of the position of the centre of gravity on the stability of

objects

Scenario Effect on stability Measure to increase stability

Higher centre of gravity • Lower stability of the object

• Toppling will occur at smaller angles of tilt

Decrease the centre of gravity by adding more mass below the current centre of gravity to the object

Object is tilted such that centre of gravity is still vertically above the base of object

Object will not topple Increase the size of base

Object is tilted such that centre of gravity is no longer vertically above the base of object

Object will topple

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6. Pressure

Content

• Pressure

• Pressure differences

• Pressure measurement

Learning Outcomes


(a) define the term pressure in terms of force and area (b) recall and apply the relationship

pressure = force / area to new situations or to solve related problems


Pressure Average force per unit area •

ForcePressure

Area=

• F

p =A

p F A A force of 4 N acting on an area of 2 m2 results in a pressure of 2 Pa

Pa or N m-2 N m2

(c) describe and explain the transmission of pressure in hydraulic systems with particular

reference to the hydraulic press

Transmission of pressure in hydraulic systems

Description

• Oil is the incompressible, high density liquid used in the transmission of pressure

• Effort piston has a smaller cross sectional area than that of the piston below the load

• Since liquid pressure at both pistons are equal when they are at the same level,

• A small force exerted on the effort piston will create a much bigger force on the load piston in comparison

Diagram Calculations

• Since water level at X is the same as the water level at Y,

• Pressure at X Pressure at Y=

• X Y

X Y

F F

A A=

• YX X

Y

FF A

A

=

• Since X YA A

• X YF F

• If the load is at Y and FY represents the weight of the load, use of the hydraulic press will require a smaller force of FX instead of FY to lift the load upwards

oil

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(d) recall and apply the relationship pressure due to a liquid column = height of column ×

density of the liquid × gravitational field strength to new situations or to solve related

problems

Term Formula SI units

Pressure due to liquid column

• Pressure due to liquid

Height of column Density of liquid Gravitational field strength=

• p h g=

p h g

N m-2 m kg m-3 N kg-1

Example of diagram of manometer Calculations

• Water level at A is the same as the water level at B

• Gas pressure at A Pressure at B=

5

Atmospheric pressure at B

1.01 10 Pa at B

= +

= +

h g

h g

(e) describe how the height of a liquid column may be used to measure the atmospheric

pressure

Diagram of barometer Description of measurement of atmospheric pressure

• Set up a barometer using high density mercury of 13.6 kg m-3

• Atmospheric pressure Pressure from mercury in glass tube=

( ) ( ) ( )3

5

0.760 13.6 9.8 10

1.013 10 Pa

=

=

=

h g

(f) describe the use of a manometer in the measurement of pressure difference

Redirect instructions

Refer to Learning Outcome 6(f) above

gas

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7. Energy, Work and Power

Content

• Energy conversion and conservation

• Work

• Power

Learning Outcomes


(a) show understanding that kinetic energy, potential energy (chemical, gravitational,

elastic), light energy, thermal energy, electrical energy and nuclear energy are examples of

different forms of energy

Examples of forms of energy

Kinetic Potential Thermal Light Electrical Nuclear

Movement Stored energy Heat

Chemical Gravitational Elastic

Food or batteries

Raised above ground

Compression or stretching of elastic objects like springs

(b) state the principle of the conservation of energy and apply the principle to new


Term Definition

Principle of conservation of energy

Energy can neither be created nor destroyed but can only be transferred from one body to another or from one form to another while total energy remains the same

(c) calculate the efficiency of an energy conversion using the formula efficiency = energy

converted to useful output / total energy input

Term Formula

Energy input Useful energy output Wasted En energy inp ergy ou uut tp t= +

Efficiency Useful energy outputEfficiency 100%

Energy input=

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(d) state that kinetic energy Ek = ½ mv2 and gravitational potential energy Ep = mgh (for

potential energy changes near the Earth’s surface) (e) apply the relationships for kinetic

energy and potential energy to new situations or to solve related problems


Kinetic energy of an object

• ( )21

2Kinetic energy Mass Speed=

• 21

2kE mv=

Ek m v

J kg m s-1

Potential energy of an object

• Gravitational potential energy

Mass Gravitational field strength Height=

• pE mgh=

Ep m g h

J kg N kg-1 m

(f) recall and apply the relationship work done = force × distance moved in the direction of

the force to new situations or to solve related problems


Work done of an object

• Force DistanceWork travdo e en de ll=

• W Fd=

W F d

J N m

(g) recall and apply the relationship power = work done / time taken to new situations or to

solve related problems


Power of an object •

Work done Energy converted

Time taken TimeP

owe

enr

tak= =

• PW E

=t t

=

P W E t

W or J s-1 J J s

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SECTION III: THERMAL PHYSICS

Overview Amongst the early scientists, heat was thought as some kind of invisible, massless fluid called ‘caloric’. Certain objects that released heat upon combustion were thought to be able to ‘store’ the fluid. However, this explanation failed to explain why friction was able to produce heat. In the 1840s, James Prescott Joule used a falling weight to drive an electrical generator that heated a wire immersed in water. This experiment demonstrated that work done by a falling object could be converted to heat. In the previous section, we studied about energy and its conversion. Many energy conversion processes which involve friction will have heat as a product. This section begins with the introduction of the kinetic model of matter. This model is then used to explain and predict the physical properties and changes of matter at the molecular level in relation to heat or thermal energy transfer.


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8. Kinetic Model of Matter

Content

• States of matter

• Brownian motion

• Kinetic model

Learning Outcomes


(a) compare the properties of solids, liquids and gases

Properties Solids Liquids Gases

Volume Fixed Fixed Not fixed

Shape Fixed Not fixed Not fixed

Compressibility No No Yes

Density High High Low

Others Usually hard and rigid Tend to form droplets N.A.

(b) describe qualitatively the molecular structure of solids, liquids and gases, relating their

properties to the forces and distances between molecules and to the motion of the

molecules

Molecular structure Solids Liquids Gases

Forces of attraction between particles

Particles held by very strong forces of attraction

Particles held by strong forces of attraction

Particles held by weak forces of attraction

Distance between particles

Packed very closely together with more particles per unit volume

Packed close to one another

Spread far apart from one another

Motion of particles Vibrate about fixed positions

Slide and move past one another randomly

Move in a constant, random and erratic manner

(c) infer from Brownian motion experiment the evidence for the movement of molecules

Term Definition Brownian motion experiment

Setup Observations Inferences

Brownian motion

Small particles suspended in a liquid or gas tend to move in random paths through the fluid even if it is calm

Place smoke particles in a container of air, suspending them in air

Smoke particles are being continuously bombarded by air molecules and move irregularly by Brownian motion

This shows that the fluids have an ability to flow or move freely

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(d) describe the relationship between the motion of molecules and temperature

Relationship between motion of molecules and temperature

• When solid or fluid (liquid / gas) is at a higher temperature, the particles vibrate or move faster respectively

• The average kinetic energy of the particles is the measure of temperature or degree of hotness

(e) explain the pressure of a gas in terms of the motion of its molecules

Explanation of pressure of a gas Effect of increasing temperature on pressure

• Molecules present in a fluid collide with the walls of the container at a constant rate

• Each collision exerts a force on the walls of the container

• As the force is acted on a particular quantity of surface area of walls, the gas exerts pressure on the walls

• When temperature is increased, molecules move faster and collide with the walls of the container more frequently

• Average force on the walls of the container increases over the same surface area of walls, thus gas pressure increases

(f) recall and explain the following relationships using the kinetic model (stating of the

corresponding gas laws is not required): (i) a change in pressure of a fixed mass of gas at

constant volume is caused by a change in temperature of the gas (ii) a change in volume

occupied by a fixed mass of gas at constant pressure is caused by a change in temperature

of the gas (iii) a change in pressure of a fixed mass of gas at constant temperature is

caused by a change in volume of the gas

Gas equation

1 1 2 2

1 2

, where : Pressure, : Volume, : Temperature, only for gasesp V p V

p V TT T

=

Cause Temperature of gas increases Volume decreases

Effect Volume increases Pressure unchanged Pressure increases Pressure increases

Condition Only if container can expand further

Only if container can expand further

Only if container cannot expand

Under all cases

Explanation • Molecules gain kinetic energy and move faster

• Gas molecules hit the container walls with higher speed

• Frequency of collisions of the gas molecules with the walls increases

• Greater force is exerted on walls, gas expands since container can expand

• Gas expands in volume since the container can expand, decreasing the number of gas particles per unit volume and increasing surface area of walls

• Number of gas particles hitting the walls per unit area decreases

• Average force exerted per unit area remains unchanged, hence a constant pressure is maintained

• Molecules gain kinetic energy and move faster

• Gas molecules hit the container walls with higher speed

• Frequency of collisions of the gas molecules with the walls increases

• Average force exerted per unit area on the container walls increases

• Gas is compressed at constant temperature and number of gas particles per unit volume increases

• Frequency of collisions of molecules with container walls increases

• Force exerted per unit area on the container increases, thus pressure increases

(g) use the relationships in (f) in related situations and to solve problems (a qualitative

treatment would suffice)

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9. Transfer of Thermal Energy

Content

• Conduction

• Convection

• Radiation

Learning Outcomes


(a) show understanding that thermal energy is transferred from a region of higher

temperature to a region of lower temperature

Thermal energy transfer

Thermal energy is transferred from a region of higher temperature to a region of lower temperature

(b) describe, in molecular terms, how energy transfer occurs in solids

Energy transfer occurs in solids In comparison with fluids

• When one region of a solid is heated, the molecules there gain kinetic energy and vibrate faster

• They collide with the slower neighbouring particles and transfer energy to them

• In fluids, the particles are further apart from each another than in liquids or gases

• Therefore kinetic energy is transferred more slowly

(c) describe, in terms of density changes, convection in fluids

Convection in fluids In comparison with solids

• Hot fluid expands and has lower density than cold fluid, causing it to rise

• Cold fluid contracts and has higher density than hot fluids, sinking to replace the hot fluid

• Convection current is set up when the cycle repeats

• Convection involves the bulk movement of fluids which carry heat with them

• Solids cannot cause convection as heat can only be transferred from one molecule to another

• The molecules are unable to flow around themselves

(d) explain that energy transfer of a body by radiation does not require a material medium

and the rate of energy transfer is affected by: (i) colour and texture of the surface (ii)

surface temperature (iii) surface area

Energy transfer of a body by radiation

• Infrared radiation is continuously emitted by all objects through their surfaces as radiation does not require a material medium for thermal transfer to occur

• When these infrared waves reach another object, the waves are transformed into heat energy, which is then absorbed by the object

• Higher surface areas, higher surface temperatures (relative to surroundings) and dull surfaces accelerate radiation of heat

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(e) apply the concept of thermal energy transfer to everyday applications

Applications Features Advantages Reasons

Styrofoam food packages

Mostly made of styrofoam

Conduction is reduced

• This is due to the presence of many air pockets

• Air is a poor conductor of heat

Covered with a lid

Convection is reduced

Convection currents are unable to be set up due to the presence of the lid compressing the contents into a closely packed arrangement

Vacuum flasks

Plastic stopper

Conduction & convection is reduced

• Plastic is a poor conductor of heat

• With a stopper, a convection current is being prevented from set up

Vacuum between the glass walls

As vacuum is unable to conduct and cause convection of heat, the amount of heat medium is decreased

Silvered glass walls

Radiation is reduced

• The shiny and smooth surface is a poor emitter and absorber of heat

• It is able to reflect heat back to the container very well

Air trapped above contents

Conduction is reduced

Air is a poor conductor of heat

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10. Temperature

Content

• Principles of thermometry

Learning Outcomes


(a) explain how a physical property which varies with temperature, such as volume of liquid

column, resistance of metal wire and electromotive force (e.m.f.) produced by junctions

formed with wires of two different metals, may be used to define temperature scales

Differences Mercury thermometer Platinum wire Thermocouple

Physical property

Volume or height of liquid column

Resistance Electromotive force (e.m.f.) produced by 2 junctions formed with wires of 2 different metals

Rationale Mercury is sensitive to changes in temperature and expands when temperature rises

• Resistance of the wire rises when temperature rises

• Voltage

ResistanceCurrent

=

E.m.f. between two substances increases when the temperature difference between them rises

Apparatus

Calculations 0

100 0

where is the value of physical property used (can be ve / ve)C 100,

and C is the temperature of the substance measured

o

o

XX X

X X

+ −−=

−

(b) describe the process of calibration of a liquid-in-glass thermometer, including the need

for fixed points such as the ice point and steam point

Calibration of liquid-in-glass thermometer Need for fixed points

• Place thermometer in ice point (funnel containing pure melting ice), then in steam point (above boiling water)

• Mark the level of mercury in both situations

• The difference in temperature of both points is 100oC

• Between the upper and lower fixed points markings, divide and mark one hundred equal divisions

• Since an increase in the temperature will increase the volume of mercury proportionately, each division is one degree Celsius

• Fixed points (ice and steam points) are used for calibration for all thermometers to agree accurately on a same temperature scale

• This is because fixed points are reproducible and will produce definite temperatures

mV

Iron Copper

0oC

s

Copper

100 C,o

then Co

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11. Thermal Properties of Matter

Content

• Internal energy

• Specific heat capacity

• Melting, boiling and evaporation

• Specific latent heat

Learning Outcomes


(a) describe a rise in temperature of a body in terms of an increase in its internal energy

(random thermal energy)

Term Meaning

Internal energy

Random thermal energy of a body resulting from the kinetic and potential energy of the particles by their movement and arrangement

Description of rise in temperature of a body

When a body is heated, its internal energy (consisting of kinetic energy and potential energy) rises

Kinetic energy Potential energy

Kinetic energy of particles increases, causing particles vibrate or move faster

• During melting and boiling, potential energy of the particles also increases

• This is since there is no rise in temperature, causing latent heat to be taken in

(b) define the terms heat capacity and specific heat capacity

Term Definition Symbol

Heat capacity Amount of heat energy required to raise the temperature of a body by 1 K or 1 °C C

Specific heat capacity

Amount of heat energy required to raise the temperature of 1 kg of a body by 1 K or 1 °C

c

(c) recall and apply the relationship thermal energy = mass × specific heat capacity ×

change in temperature to new situations or to solve related problems


Thermal energy when there is a temperature change

• Thermal energy

Mass Specific heat capacity Change in temperature=

• Heat ( )( )( )m c =

m c

kg J kg-1 oC-1

or J kg-1 K-1

oC or K

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(d) describe melting/solidification and boiling/condensation as processes of energy transfer

without a change in temperature

Term Meaning

Melting Process of energy transfer from the surroundings to a solid to turn it to a liquid without a change in temperature

Solidification Process of energy transfer from a liquid to the surroundings to turn it to a solid without a change in temperature

Boiling Process of energy transfer from the surroundings to a liquid to turn it to a gas without a change in temperature

Condensation Process of energy transfer from a gas to the surroundings to turn it to a liquid without a change in temperature

(e) explain the difference between boiling and evaporation

Description of evaporation

• At any temperature, the molecules of liquid are in continuous random motion with different speeds

• Some more energetic molecules near to the surface of the liquid have enough energy to overcome the attractive forces of other molecules and escape

• They evaporate from the liquid to form a vapour

Differences Boiling Evaporation

Temperature Occurs at a fixed temperature Occurs at any temperature

Location Occurs throughout the liquid Occurs at the surface of the liquid

Heat source Heat is supplied from an energy source Heat is supplied by the surroundings

(f) define the terms latent heat and specific latent heat

Term Definition

Latent heat Heat energy released or absorbed during a change of state to make or break intermolecular forces of attraction without any change in temperature

Latent heat of fusion Heat energy required to change a solid to its liquid state or vice versa without any change in temperature

Latent heat of vapourisation

Heat energy required to change a liquid to its vapour state or vice versa without any change in temperature

Specific latent heat Heat energy required to change 1 kg of a substance from one state to another or vice versa without any change in temperature

(g) recall and apply the relationship thermal energy = mass × specific latent heat to new



Thermal energy when there is no temperature change

• Thermal energy Mass Specific latent heat=

• Latent heat ( )( )fm=

m f

kg J kg-1

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(h) explain latent heat in terms of molecular behaviour

Term Definition

Latent heat Heat energy released or absorbed during a change of state to make or break intermolecular forces of attraction without any change in temperature

(i) sketch and interpret a cooling curve

Sketch of cooling curve of water Interpretation of cooling curve

Description Explanation

Decreases in temperature during gas, liquid and solid state in the graph

This is because thermal energy is being released with no change in intermolecular forces of attraction between the molecules

No change in temperature during condensation and freezing until all the water vapour has condensed and all the water has frozen

This is because thermal energy is being released to form greater intermolecular forces of attraction between the molecules such that there is a state change

condensation

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SECTION IV: WAVES

Overview Waves are inherent in our everyday lives. Much of our understanding of wave phenomena has been accumulated over the centuries through the study of light (optics) and sound (acoustics). The nature of oscillations in light was only understood when James Clerk Maxwell, in his unification of electricity, magnetism and electromagnetic waves, stated that all electromagnetic fields spread in the form of waves. Using a mathematical model (Maxwell’s equations), he calculated the speed of electromagnetic waves and found it to be close to the speed of light, leading him to make a bold but correct inference that light consists of propagating electromagnetic disturbances. This gave the very nature of electromagnetic waves, and hence its name. In this section, we examine the nature of waves in terms of the coordinated movement of particles. The discussion moves on to wave propagation and its uses by studying the properties of light, electromagnetic waves and sound, as well as their applications in wireless communication, home appliances, medicine and industry.


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12. General Wave Properties

Content

• Describing wave motion

• Wave terms

• Longitudinal and transverse waves

Learning Outcomes


(a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs

and by waves in a ripple tank

Term Definition

Wave motion Propagation of waves through a medium by the vibration of particles in the wave transmitting energy

Illustrations Transverse waves Longitudinal waves

Rope

N.A.

Spring

Ripple tank

N.A.

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Comparison of waves in a ripple tank

Description Waves of water undergo refraction when it travels from deeper water to shallower water or vice versa

Differences Deeper water Shallower water Illustrations

Wavelength Increases Decreases

Velocity Increases Decreases

Frequency Remains the same Remains the same

Direction Away from the normal Towards the normal

Wavefront Perpendicular to direction of wave

Perpendicular to direction of wave

(b) show understanding that waves transfer energy without transferring matter

Waves

• A wave is the collective motion of many particles

• Occurs when particles of the medium move in a specific manner

What is transferred What is not transferred

Energy Medium

(c) define speed, frequency, wavelength, period and amplitude


Frequency The number of complete waves produced per second by a source 1f

T=

Period The time taken to produce one complete wave 1T

f=

Wavelength Shortest distance between any two points of a wave in phase Represented by

(Refer to diagram)

Speed Distance travelled by a crest or rarefraction per unit time by a wave v f=

Amplitude Maximum displacement of crest or rarefaction from the rest position Refer to diagram

Diagram

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(d) state what is meant by the term wavefront

Term Definition

Wavefront Imaginary line on a wave that joins all points that are in the same phase

(e) recall and apply the relationship velocity = frequency × wavelength to new situations or

to solve related problems


Velocity of wave • Velocity Frequency Wavelength=

• v f=

v f

m s-1 Hz m

(f) compare transverse and longitudinal waves and give suitable examples of each

Term Definition Properties

Transverse wave

Waves that travel in a direction perpendicular to the direction of vibration of the particles

Crests and troughs represent amplitude and minimum displacement respectively

Longitudinal wave

Waves that travel in a direction parallel to the direction of vibration of the particles

Rarefactions and compressions represent amplitude and minimum displacement respectively

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13. Light

Content

• Reflection of light

• Refraction of light

• Thin lenses

Learning Outcomes


(a) recall and use the terms for reflection, including normal, angle of incidence and angle of

reflection

Ray diagram Legend

mirror

• i represents the angle of incidence

• r represents the angle of reflection

(b) state that, for reflection, the angle of incidence is equal to the angle of reflection and use

this principle in constructions, measurements and calculations

Reflection laws Features of a plane mirror image

• Angle of incidence is equal to angle of reflection

• The normal, incident ray and reflected ray all lie in the same plane

Features Acronym

• Virtual

• Image is the same size as the object (Size)

• Image as far away from the mirror as the object is from the mirror (Far)

• Laterally inverted

• Upright

VS FLU

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(c) recall and use the terms for refraction, including normal, angle of incidence and angle of

refraction

Term Meaning Conditions Remark

Refraction • Refers to the change in direction or bending of light when it passes from one medium to another medium of different optical densities due to the change in speed of light

• The light ray bends towards the normal when travelling into a medium of higher optical density

• The light ray bends away from the normal when travelling into a medium of lower optical density

• Angle of incidence must not be 0o

• If ray travels from a denser to less dense medium, angle of incidence must be less than critical angle

‘Density’ in this case represents optical density

Ray diagram Real and apparent depth Legend


• r represents the angle of refraction

(d) recall and apply the relationship sin i / sin r = constant to new situations or to solve

related problems (e) define refractive index of a medium in terms of the ratio of speed of

light in vacuum and in the medium

Term Definition Formula Legend

Refractive index of a medium

The constant ratio of the speed of light in vacuum to the speed of light in the medium

Speed of light in vacuum

Speed of light in mediumn =

sin (from vacuum to medium)

sin =

i

r sin

(from medium to vacuum)sin

=r

i

Real depth

Apparent depth=

• n represents refractive index


• r represents the angle of refraction

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(f) explain the terms critical angle and total internal reflection


Critical angle

The angle of incidence of a ray in the optically denser medium whereby the angle of refraction of it in the optically less dense medium is 90o

-1 sin 90sin ,

sin sin

1 1c n

n c c

= =

=

Total internal reflection

Reflection of light rays within the optically denser medium when the angle of incidence in the optically denser medium is more than the critical angle

N.A.

Illustrative diagrams

Refraction Critical angle Total internal reflection

• i represents the angle of incidence which is less than critical angle

• r represents the angle of refraction which is within the optically less dense medium and is less than 90o

• i represents the angle of incidence which is equal to critical angle

• r represents the angle of refraction which is along the boundary of the 2 mediums and is equal to 90o

• i represents the angle of incidence which is more than critical angle

• r represents the angle of reflection which is within the optically denser medium and is equal to i

(g) identify the main ideas in total internal reflection and apply them to the use of optical

fibres in telecommunication and state the advantages of their use

Main ideas in total internal reflection

• Light ray has to travel from denser medium towards the less dense medium

• Angle of incidence of light ray is more than critical angle

• The light ray will reflect internally by the laws of reflection within the denser medium

Optical fibres in telecommunications

Advantages Diagram

• Light pulses carry telecommunications data at a faster rate

• Less data loss compared to use of copper wires

• Optical fibres are generally cheaper and lighter than copper wires

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(h) describe the action of a thin lens (both converging and diverging) on a beam of light

Differences Converging lens Diverging lens

Lens type Convex lens Concave lens

Light rays

Ray diagram

Description of lens action

▪ The lens is curved, ▪ thus the angles of incidence of parallel rays

of light differ, ▪ causing the rays to change direction

differently after passing through the lens

▪ The lens is curved, ▪ thus the angles of incidence of parallel

rays of light differ, ▪ causing the rays to change direction

differently after passing through the lens

• The front of the lens facing the incident light rays curve outwards

• The light rays converge at a common focal point

• The front of the lens facing the incident light rays curve inwards

• The light rays diverge from one another

(i) define the term focal length for a converging lens

Term Definition Diagram

Focal length of converging lens

Distance between the optical center and the principal focus, where parallel rays of light converge after passing through the lens

focal length

optical center

principal focus

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(j) draw ray diagrams to illustrate the formation of real and virtual images of an object by a

thin converging lens

# Object location Image location Image properties Acroynm Uses

1 u = v f= Diminished, inverted, real DIR Telescope

2 2u f 2f v f Diminished, inverted, real DIR • Camera

• Eye

3 2u f= 2v f= Same size, inverted, real SIR Photocopier

4 2f u f 2v f Magnified, inverted, real MIR Projector

5 u f= v = Magnified, upright, virtual MUV Spotlight

6 u f 2f v f− − Magnified, upright, virtual MUV • Magnifying glass

• Spectacles

Image formation based on object location

# 1 2

Object location

u = 2u f

Ray diagram

# 3 4

Object location

2u f= 2f u f

Ray diagram

# 5 6

Object location

u f= u f

Ray diagram

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14. Electromagnetic Spectrum

Content

• Properties of electromagnetic waves

• Applications of electromagnetic waves

• Effects of electromagnetic waves on cells and tissue

Learning Outcomes


(a) state that all electromagnetic waves are transverse waves that travel with the same

speed in vacuum and state the magnitude of this speed

# Point Property of electromagnetic waves (EM waves)

1 Type • Transverse waves

• Electric and magnetic fields oscillate 90o to each other

2 Laws They obey the laws of reflection and refraction

3 Electric charge No electric charge is carried through EM waves

4 Medium No medium is required and the wave can travel through vacuum

5 Frequency Remains the same all the time

6 Wavelength Decreases from optically less dense to denser medium

7 Velocity • 3 x 108 ms-1 in vacuum, slows down in matter

• Decreases from optically less dense to denser medium

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(b) describe the main components of the electromagnetic spectrum (c) state examples of

the use of the following components: (i) radiowaves (e.g. radio and television

communication) (ii) microwaves (e.g. microwave oven and satellite television) (iii) infra-red

(e.g. infra-red remote controllers and intruder alarms) (iv) light (e.g. optical fibres for

medical uses and telecommunications) (v) ultra-violet (e.g. sunbeds and sterilisation) (vi) X-

rays (e.g. radiological and engineering applications) (vii) gamma rays (e.g. medical

treatment)

Component Frequency Applications Description

Radio waves 1× 10^ 8 Hz Radio and television communications

Able to go around obstructions (due to longer wavelengths)

Microwaves 1× 10^ 10 Hz Microwave oven Water molecules vibrate millions of times a second to produce heat from friction

Satellite television Can penetrate haze, light rain, snow, clouds and smoke with proper alignment

Infra-red 1× 10^ 12 Hz Remote controllers −

Intruder alarms Alarm rings when it receives infra-red radiation an intruding human gives out

Light (Red) 5× 10^ 14 Hz Medical optical fibres −

(Violet) Telecommunications −

Ultra-violet 3× 10^ 16 Hz Sunbeds Artificial tanning (shorter frequency UVA)

Sterilisation Germicidal lamps (longer frequency UVB/C)

X-rays 3× 10^ 18 Hz • Diagnose fractures

• Airport scanners

Can penetrate through all materials other than lead, thus may be applied using X-ray imagery

Gamma rays 3× 10^ 20 Hz Cancer treatment Kill cancer cells in cancerous tumours (high energy waves)

Changes in the EM spectrum from radio to gamma waves

Frequency Wavelength

Increases from radio waves to gamma rays Decreases from radio waves to gamma rays

(d) describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and

damage to living cells and tissue

Effects of absorbing electromagnetic waves

Infrared High energy EM waves X-rays

• Human skin absorbs infrared waves from BBQ pits

• Human bodies will receive the radiation and be heated to feel warm

• EM waves of frequencies higher than light have high energy causing ionisation

• Ionisation of living matter in human bodies damages chromosomes, living cells and tissues

• Overexposure leads to premature ageing and lifespan shortening

• Overexposure of developing fetus to X-ray imagery can cause abnormal cell division

• A deformed baby and leukemia may result

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15. Sound

Content

• Sound waves

• Speed of sound

• Echo

• Ultrasound

Learning Outcomes


(a) describe the production of sound by vibrating sources (b) describe the longitudinal

nature of sound waves in terms of the processes of compression and rarefaction

Production of sound in air Description of sound waves

A vibrating source causes particles in air to be displaced, moving away and from the source continuously

• Air particles oscillate left and right to produce compressions at high air pressure and rarefactions at low air pressure

• A longitudinal sound wave is produced

(c) explain that a medium is required in order to transmit sound waves and the speed of

sound differs in air, liquids and solids

Conditions for transmission of sound waves Approximate speeds of sound

• A vibrating source must be present

• The source must be placed in a medium

• Energy transmitted by sound waves depends on its frequency and amplitude

• Speed of sound increases from gas to solid

In gases Air 330 m s-1

In liquids Water 1500 m s-1

In solids Iron 5000 m s-1

Steel 6000 m s-1

(d) describe a direct method for the determination of the speed of sound in air and make the

necessary calculation

Experiment to determine speed of sound in air

Method Calculation Reliability

• Observers A and B are positioned at a far distance apart, S, to minimise human reaction error

• Observer A fires a pistol and Observer B starts the stopwatch on seeing the flash of the pistol

• He stops the stopwatch when he hears the sound

• The time interval between the two actions, T, is recorded

Speed of sound is calculated by the following formula:

SpeedS

T=

• For better accuracy, the experiment is repeated and the average speed of sound is calculated

• The experiment is further repeated by interchanging the positions of Observers A and B to minimise the effects of wind

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(e) relate loudness of a sound wave to its amplitude and pitch to its frequency

Cause Frequency increases Amplitude increases

Effects on Pitch Increases Remains the same

Loudness Remains the same Increases

(f) describe how the reflection of sound may produce an echo, and how this may be used

for measuring distances

Experiment to measure distances using echoes

Theory Method Calculation Reliability

• Sound waves follow the laws of reflectlon

• The harder and larger the surface is, the stronger the echo

• When sound waves are reflected after striking objects, the reflected sound, an echo, is produced

• When a source emits a sound and then receives an echo, the sound must have travelled a distance of 2D, where D is the distance between the source and the reflected surface

• The time interval between emission and receiving of the sound is recorded as T

• The speed of sound in the medium is labelled as V

Distance from source and reflected surface is calculated by the following formula:

TVD

2=

For better accuracy, the experiment is repeated and the average distance is calculated

Example of measuring distances using echoes (depth of seabed)

Diagram Calculation

-1

Let be the depth of the seabed,

be the duration between sound emission and echo receival,

and be the speed of sound in water, which is 1500 ms

2d

T

V

• Total distance travelled by sound 2d TV= =

• 1500

750TV T

d T2 2

= = =

(g) define ultrasound and describe one use of ultrasound, e.g. quality control and pre-natal

scanning

Term Definition Uses Description Mechanism

Ultrasound Sound with waves above 20 kHz frequency, which is above the upper limit of the human hearing range

(Humans can only hear sound of frequencies between 20 Hz to 20 kHz)

Quality control

▪ Manufactures of various concrete types

▪ check for cracks or cavities in concrete slabs with ultrasound

▪ to ensure that their concrete are of the highest quality

▪ Ultrasound is released from an emitter at one end of the concrete slab and

▪ a sensor is positioned at the other end to detect the ultrasound

▪ If the speed of sound recorded is lower than actual, this means parts of the concrete contain air

Pre-natal scanning

▪ Ultrasound can be used to obtain images of inside a body,

▪ thus is used to examine development of a foetus in a pregnant woman

▪ Ultrasound pulses are sent into the body using a trasmitter

▪ Echoes reflected from any surface within the body are received

▪ The time interval is noted to determine the depth of the reflecting surface within the body

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SECTION V: ELECTRICITY AND MAGNETISM

Overview For a long time, electricity and magnetism were seen as independent phenomena. Hans Christian Oersted, in 1802, discovered that a current carrying conductor deflected a compass needle. This discovery was overlooked by the scientific community until 18 years later. It may be a chance discovery, but it takes an observant scientist to notice. The exact relationship between an electric current and the magnetic field it produced was deduced mainly through the work of Andre Marie Ampere. However, the major discoveries in electromagnetism were made by two of the greatest names in physics, Michael Faraday and James Clerk Maxwell. The section begins with a discussion of electric charges that are static, i.e. not moving. Next, we study the phenomena associated with moving charges and the concepts of current, voltage and resistance. We also study how these concepts are applied to simple circuits and household electricity. Thereafter, we study the interaction of magnetic fields to pave the way for the study of the interrelationship between electricity and magnetism. The phenomenon in which a current interacts with a magnetic field is studied in electromagnetism, while the phenomenon in which a current or electromotive force is induced in a moving conductor within a magnetic field is studied in electromagnetic induction.

Extracted from CHEMISTRY GCE ORDINARY LEVEL (2014) Syllabus Document

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16. Static Electricity

Content

• Laws of electrostatics

• Principles of electrostatics

• Electric field

• Applications of electrostatics

Learning Outcomes


(a) state that there are positive and negative charges and that charge is measured in

coulombs

Charge

Types Measurement

• Positive

• Negative

• Charge is measured in coulombs (C)

• For example, one negative electron has a charge of 1.6 x 10-19 C

(b) state that unlike charges attract and like charges repel

Interaction of charges

Combination of charges Interaction

Unlike charges Positive-negative Attract

Like charges Positive-positive Repel

Negative-negative

(c) describe an electric field as a region in which an electric charge experiences a force (d)

draw the electric field of an isolated point charge and recall that the direction of the field

lines gives the direction of the force acting on a positive test charge

Term Definition

Electric field Region in which an electric charge experiences a force

Electric field lines Gives direction of the electric field (i.e. direction of the force on a small positive charge)

Electric field of an isolated point charge

Positive charge Negative charge

Diagram

Field lines From charge Towards charge

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(e) draw the electric field pattern between two isolated point charges

Electric field of an isolated point charge

Positive-negative Positive-positive Negative-negative

▪ Opposite charges attract, ▪ hence the two charges are linked by field lines

▪ Like charges repel, ▪ hence no field lines connect the two charges

Electric field of parallel charged plates

(f) show understanding that electrostatic charging by rubbing involves a transfer of

electrons

Experimental method of rubbing (to show electrostatic charging between 2 uncharged materials)

Action Result

Rub two different materials against each other

• Some negatively charged electrons are transferred from one material to the other

• An object becomes negatively charged if it gains electrons and positively charged if it loses electrons

Ease of loss of electrons between objects

Ease of loss of electrons generally decreases down the following list:

Electron loss Object type Examples Electron transfer

Easiest Transparent object Glass, Perspex

Smooth, high surface area object Silk, Fur, Hair, Wool

Hardest Opaque object Ebonite, Rubber, Polyethene

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(g) describe experiments to show electrostatic charging by induction

Experimental method of induction (to show electrostatic charging of a single metal conductor)

# Action Result Diagram

1 To negatively charge a neutral conductor, bring a positively charged rod near it

• Like charges repel and unlike charges attract each other

• Thus the positively charged rod leaves an excess of negative charges at the side of conductor nearest to the rod and positive charges at the other side by induction

2 Earth the side of the conductor with the positive charges

Electrons flow from Earth to the conductor to neutralise the positive charges

3 Remove the Earth, then the rod

Electron migration causes the rod to be completely negatively charged

Experimental method of induction (to show electrostatic charging of 2 metal spheres)

# Action Result

1 • Let the two conductors (metal spheres on insulating stands) touch each other

• Bring a negatively charged rod near the conductor on the left

▪ The negatively charged rod induces the charges in the two conductors,

▪ repelling the negative charges to the furthest end of the conductor on the right,

▪ leaving excess positive charges at the end of conductor on the left nearest to the rod

2 • Separate the two conductors far from each other

• Remove the rod

• The conductor on the left will be positively charged

• while the other on the right will be negatively charged

(h) describe examples where electrostatic charging may be a potential hazard

Potential hazards of electrostatic charging

Lightning Electrostatic discharge

• Friction between water molecules in thunderclouds and air molecules in the air cause the thunderclouds to be charged

• Air is ionised when the charge on the thunderclouds becomes large enough

• The ionised air provides a conducting path for the huge quantity of electric charge on the thunderclouds to the nearest object or sharpest object on the ground via lightning strikes during a sudden discharge

• Electrostatic charging is thus a potential hazard for people when they are out in an open field or under a tall tree during a thunderstorm, especially in the absence of a lightning conductor

Friction between objects may cause excessive charges to build up in them:

• Friction between tyres of a truck and the road can result in sudden discharge

• Sparks and subsequent ignition of flammable items on the truck may occur when this happens

• Friction between electronic equipment (e.g. computer boards, hard drives) and other objects can result in electrostatic discharges over time

• These electronic equipment may be damaged as this happens

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(i) describe the use of electrostatic charging in a photocopier, and apply the use of

electrostatic charging to new situations

Components of the photocopier

Photoreceptor drum Laser assembly Toner Fuser

• Metal drum roller

• Coated with a photoconductive layer

• Laser

• Movable mirror

• Lens

Fine negatively charged powder Heat source

Electrostatic charging in a photocopier

# Action Result Diagram

1 A photoreceptor drum is rotated near a highly positively charged corona wire

The photoreceptor drum becomes positively charged

2 The laser beam is cast over a page of the original document through a lens onto the photoreceptor drum

• Areas of photoconductive layer on the drum surface that are exposed to the laser is discharged

• Negatively charged toner is then attracted to the remaining positively charged areas

3 • Toner on the drum is transferred to the paper

• Paper is heated by the fuser

Toner power melts onto the paper surface, affixing itself permanently on the surface

Note: A laser printer operates differently from a photocopier, although both rely on electrostatic charging

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17. Current of Electricity

Content

• Conventional current and electron flow

• Electromotive force

• Potential difference

• Resistance

Learning Outcomes


(a) state that current is a rate of flow of charge and that it is measured in amperes

Term Definition Measurement Formula SI units

Current A measure of the rate of flow of electric charge through a cross section of a conductor

• Ammeter

• Connected in series

• Charge

CurrentTime

=

• Q

It

=

I Q t

A C s

(b) distinguish between conventional current and electron flow

Conventional current flow Electron flow Combined flow of charges

Flow of positive charges from a positively charged end to a negatively charged end (i.e. current)

Flow of electrons from a negatively charged end to a positively charged end

(c) recall and apply the relationship charge = current × time to new situations or to solve

related problems

Term Definition Formula SI units

Charge • When an object is charged, it is electrified

• Equals to the product of current and time

• Charge Current Time=

• Q It=

Q I t

C A s

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(d) define electromotive force (e.m.f.) as the work done by a source in driving unit charge

around a complete circuit


Electro-motive force

Work done by an electrical source in driving a unit charge round a complete circuit

• Voltmeter

• Connected in parallel across the positive and negative ends of the electrical source

• E.m.f.

Electrical energy converted

Charge=

• W

Q =

W Q

V J C

(e) calculate the total e.m.f. where several sources are arranged in series

Example of circuit of 3 dry cells as sources

Diagram Readings recorded Total e.m.f.

Voltmeter Dry cell e.m.f. Total e.m.f. of all dry cells

Sum of all e.m.f. of each dry cell

1.5 1.5 3

6 V

=

= + +

=

1 1.5 V

2 1.5 V

3 3 V

(f) state that the e.m.f. of a source and the potential difference (p.d.) across a circuit

component is measured in volts (g) define the p.d. across a component in a circuit as the

work done to drive unit charge through the component

(h) state the definition that resistance = p.d. / current (i) apply the relationship R = V/I to new


Term Definition Factors Formula 1 SI units

Resistance Ratio of the potential difference across a component to the current flowing through it

• Length

• Cross sectional area

• Type of material


ResistanceCurrent

=

• V

RI

=

R V I

Ω or ohm V A


Potential difference

Amount of energy converted to other forms of energy when one coulomb of positive charge passes between 2 reference points

• Voltmeter

• Connected in parallel across the 2 points


Electrical energy converted

Charge=

• W

VQ

=

Q t

A C s

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(j) describe an experiment to determine the resistance of a metallic conductor using a

voltmeter and an ammeter, and make the necessary calculations

Experiment to determine resistance of a metallic conductor

Method Calculation

• Connect a dry cell, rheostat and ammeter in series to the metallic conductor

• In the same circuit, connect a voltmeter in parallel to the metallic conductor

• Vary the resistance of the rheostat and and note down values of V (reading of voltmeter) and I (reading of ammeter) for at least 5 sets of readings

By Ohm’s law, resistance R will be equivalent to the voltage divided by current

VR

I=

Hence, plot a graph of V against I to find the gradient of the graph, R

(k) recall and apply the formulae for the effective resistance of a number of resistors in

series and in parallel to new situations or to solve related problems

Differences Resistors in series Resistors in parallel

Circuit diagram

where R1 and R2 are the resistances of the resistors respectively

where R1 and R2 are the resistances of the resistors respectively

Formula for effective resistance for the circuit above

1 2effR R R= + • 1 2

1 1 1

effR R R= +

•

1

1 2

1 1effR

R R

−

= +

Nature of effective resistance

1

2

eff

eff

R R

R R

1

2

eff

eff

R R

R R

General formula for effective resistance

1 ...eff nR R R= + + 1

1

1 1...eff

n

RR R

−

= + +

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(l) recall and apply the relationship of the proportionality between resistance and the length

and cross-sectional area of a wire to new situations or to solve related problems

Differences Resistance of material Resistivity of material

Main formula VR

I=

RA =

l

Unit Ω

Ω m

Nature • Resistance increases as length increases

• Resistance increases as cross-sectional area decreases

Independent of length & cross-sectional area

Term Formula 2 SI units Relationships

Resistance •

Wire lengthResistance Resistivity

Cross-sectional area=

• RA

= l

R l A • R l

• 1

RA

Ω Ω m m m2

(m) state Ohm’s Law

Law Definition Relationship

Ohm’s Law

Current passing through a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions are constant

• I V

• constantV

RI= =

(n) describe the effect of temperature increase on the resistance of a metallic conductor

Effect of temperature increase on resistance Explanation

Resistance of metallic conductor increases • Particles in metallic conductor gain kinetic energy and vibrate faster

• This causes electrons moving through the conductor to slow down

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(o) sketch and interpret the I/V characteristic graphs for a metallic conductor at constant

temperature, for a filament lamp and for a semiconductor diode

Differences Ohmic conductors Non-ohmic conductors (examples)

Filament lamp Semiconductor diode

Purpose N.A. Provides light indoors and at night

Allows current to flow in only one direction (i.e. forward direction) through the circuit

I/V sketch

V/I sketch

(invert the I/V sketch along the line V=I)

Interpretation Ohmic conductors follow Ohm’s law

The filament lamp is a non-ohmic conductor

The semiconductor diode is another non-ohmic conductor

Gradient V/I is constant since I is directly proportional to V

• Gradient V/I increases as V increases across the lamp

• This is because as p.d. increases, the current increases less than proportionately

• This indicates that resistance of the lamp increases as p.d. increases

• Gradient V/I decreases as V increases from zero

• This is because as p.d. increases, the current increases more than proportionately

• This indicates that resistance decreases when p.d. in the forward direction increases, allowing a relatively large current, I, to flow through

• Gradient V/I is very large as V increases to zero

• This indicates that resistance is very high when p.d. in the reverse direction increases

• Almost no current flows in this reverse direction

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18. D.C. Circuits

Content

• Current and potential difference in circuits

• Series and parallel circuits

• Potential divider circuit

• Thermistor and light-dependent resistor

Learning Outcomes


(a) draw circuit diagrams with power sources (cell, battery, d.c. supply or a.c. supply),

switches, lamps, resistors (fixed and variable), variable potential divider (potentiometer),

fuses, ammeters and voltmeters, bells, light-dependent resistors, thermistors and light-

emitting diodes

Symbols of power sources Symbols of common components

Cell Battery D.C supply A.C. supply Lamp Bell Switch Fuse

Symbols of resistors and diodes

Fixed resistor Variable resistor Thermistor Light-dependent resistor Light-emitting diode

Symbols of measurement devices Symbols of other devices

Ammeter Voltmeter Potentiometer

Circuit diagram example

Experimental setup Circuit diagram

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(b) state that the current at every point in a series circuit is the same and apply the principle

to new situations or to solve related problems (c) state that the sum of the potential

differences in a series circuit is equal to the potential difference across the whole circuit

and apply the principle to new situations or to solve related problems (d) state that the

current from the source is the sum of the currents in the separate branches of a parallel

circuit and apply the principle to new situations or to solve related problems (e) state that

the potential difference across the separate branches of a parallel circuit is the same and

apply the principle to new situations or to solve related problems

Circuit Current in circuit Potential difference across whole circuit

Series Same at every point Sum of potential differences in circuit

Parallel Sum of currents in the separate branches Same as across the separate branches

(f) recall and apply the relevant relationships, including R = V/I and those for current,

potential differences and resistors in series and in parallel circuits, in calculations involving

a whole circuit

Term Formula SI units Remarks

Resistance •

Potential differenceResistance

Current=

• V

RI

=

R V I When the circuit has resistors in both the series and parallel arrangement, calculate effective resistance of the ones arranged in parallel first

Ω or ohm V A

(g) describe the action of a variable potential divider (potentiometer)

Purpose of potentiometer Action of potentiometer

A potentiometer is able to divide the supply voltage in any ratio that is required by varying resistance and

using the formula V IR=

• The potentiometer is made of a conducting slider in contact with a resistor with fixed cross-sectional area

• By sliding the slider along the resistor, the length of the resistance material that the current of the circuit has to flow through can be varied

• Since R l , resistance of the circuit increases when the length increases

• As V IR= , potential difference across the circuit can thus be adjusted between zero and the maximum supply voltage

(h) describe the action of thermistors and light-dependent resistors and explain their use as

input transducers in potential dividers (i) solve simple circuit problems involving

thermistors and light-dependent resistors

Input tranducers

Transducers that convert non-electrical energy to electrical energy

Differences Thermistor Light-dependent resistor

Device A device whose resistance decreases when temperature increases

A device whose resistance decreases as the amount of light shining on it increases

Applications • Temperature control

• Temperature measurement in fire alarms

Under bright lighting, the LDR would have very low resistance, and vice versa

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19. Practical Electricity

Content

• Electric power and energy

• Dangers of electricity

• Safe use of electricity in the home

Learning Outcomes


(a) describe the use of the heating effect of electricity in appliances such as electric kettles,

ovens and heaters

Use of electricity Description of use

• Heating effect

• Used in heating appliances like electric kettles, ovens and heaters

• Heating elements in heating appliances musthave high resistivity (high resistance per unit length of material of constant cross-sectional area) and must be able to withstand high temperatures

• When current passes through these elements (e.g. nichrome) in heating appliances when, much heat is generated

• By varying current passing through, heat produced by Joule heating can be effectively controlled

(b) recall and apply the relationships P = VI and E = VIt to new situations or to solve related

problems

Term Formula SI units Derivation of formulae

Electrical energy • Energy Current Voltage Time=

• E VIt=

E V I t P VI= is derived from:

• Q

I Q Itt

= =

• W

V W VQ VItQ

= = =

• W VQ VIt

P VIt t t

= = = =

J V A s

Electrical power • Power Current Voltage=

• P VI=

P V I

W V A

(c) calculate the cost of using electrical appliances where the energy unit is the kW h


Electrical energy • Energy Power Time=

• E Pt=

E P t

kWh kW h

Cost of using electrical appliances Cost Energy Rate= Cost Energy Rate

¢ kWh ¢ per kWh

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(d) compare the use of non-renewable and renewable energy sources such as fossil fuels,

nuclear energy, solar energy, wind energy and hydroelectric generation to generate

electricity in terms of energy conversion efficiency, cost per kW h produced and

environmental impact

Energy source

Renewability Energy conversion

Source Efficiency Reasons

Fossil fuels Non-renewable

Chemical potential energy

30-40% Good distribution system of electricity from fossil fuels in many countries

Nuclear energy

Non-renewable

Nuclear energy 30-40% Only a small amount of uranium is needed to generate a large amount of energy

Solar energy Renewable Light energy 10-20% Efficiency is high only when there is daylight and minimal cloud cover

Wind energy Renewable Kinetic energy 30-40% Wind direction and speed varies

Hydroelectric generation

Renewable Gravitational potential energy

90% Water flow

• is concentrated

• can be easily controlled

Non-renewable energy sources

Energy source Cost per kWh produced Environmental impact

Fossil fuels High costs due to

• lower availability of fossils

• higher energy demand

Gases produced as a result of the combustion of fossil fuels are usually pollutive (e.g. may combine with rain to form acid rain)

Nuclear energy Radioactivity, when leaked, is very expensive to clean up

• Radioactivity, when leaked, is difficult and expensive to clean up

• Threat to safety as it can cause mutations to humans

Non-renewable energy sources

Energy source

Cost per kWh produced Environmental impact

Cons Pros Cons Pros

Solar energy High costs involved in manufacturing Cost of fuel (i.e. sunlight) is free

Clean energy

Large areas must be cleared to make space for the solar panels

Wind energy Falling costs due to technological improvements

Cost of fuel (i.e. wind) is free

Clean energy

Spinning turbines cause noise pollution

Hydroelectric generation

High costs involved in

• constructing the dam and power plant together

• maintanence in clearing of slit blocking water flow behind the dam

N.A. Clean energy

Dams built may disrupt ecosystems

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(e) state the hazards of using electricity in the following situations: (i) damaged insulation (ii)

overheating of cables (iii) damp conditions

Hazards of using electricity

Damaged insulation Overheating cables Damp conditions

• If one touches the exposed live wire, electrons flow through the body to Earth

• May cause severe electric shock, injury and death

• Many electrical appliances used concurrently

• Total power drawn from the mains supply may be very large

• Wires not thick enough will produce high resistance producing more heat

• Cable becomes overheated to result in a fire

• Water is a good conductor of electricity

• Provides conducting path for large current to flow

• Since the human body has very low resistance

• Human body is electrocuted when current of more than 50 mA flows through

(f) explain the use of fuses and circuit breakers in electrical circuits and of fuse ratings

Safety devices

Use of fuses Use of circuit breakers

• Internal wire melts when excessive current flows through

• The fuse rating on a fuse indicates the maximum current that can flow through it before the fuse starts to melt

• Protects electrical appliances from damage

• Ensures safety of the user

• Switches off electrical supply in a circuit when there is overflow of current

• The miniature circuit breaker trips when there is a fault in the circuit

• The Earth leakage circuit breaker switches off all circuits in the house when there is an Earth leakage of more than 25 mA from the live to earth wire

Must be replaced May be reset after problem is resolved

(g) explain the need for earthing metal cases and for double insulation

Safety precautions

Need for earthing metal cases Need for double insulation

• In case the live wire comes into contact with the metal casing by accident, someone who touches the casing will be electrocuted

• To ensure the safety of the user, the metal casing is earthed

• An earth wire is connected to casing to conduct current away to the earth directly instead of going through the human body

• Appliances with plugs of two pins have no earth wire

• Double insulation insulates electric cable from internal components and insulates the internal components from external casing of these appliances

(h) state the meaning of the terms live, neutral and earth

Term Meaning

Live Wire which delivers electrical energy to appliance at high voltage, allowing the appliance to function

Neutral Wire kept at zero volts which forms a current flow path back to the supply to complete the circuit

Earth Low resistance wire which connects the metal casing of an equipment to Earth, earthing the appliance continuously to ensure electrical safety of the user in case the metal casing becomes live

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(i) describe the wiring in a mains plug

Wiring in a mains plug Description

The cable is made up of 3 wires: the live, netural and earth wires

Wire Colour Explanation

Live Brown • Wired into the pin on the right

• A fuse is placed between the live terminal and the live pin in the circuit

• The fuse breaks the circuit if too much current flows

Neutral Blue Wired into the pin on the left

Earth Green and yellow stripes

Wired into the pin on the top

(j) explain why switches, fuses, and circuit breakers are wired into the live conductor

Wiring of safety devices Explanation

Switches, fuses and circuit breakers are wired into the live conductor

• Switches, fuses and circuit breakers work by breaking an electric circuit

• By being wired into live conductor, it will be able to prevent current flow from flowing into the conductor at all

• Damage to the conductor is prevented

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20. Magnetism

Content

• Laws of magnetism

• Magnetic properties of matter

• Magnetic field

Learning Outcomes


(a) state the properties of magnets

# Properties of magnets

Aspect Description of property

1 Magnetic poles Have magnetic poles, where the magnetic effects are strongest

2 Alignment when suspended freely Align themselves to the north and south poles of the Earth when suspended freely

3 Interaction with magnetic materials Attract magnetic materials, which are iron, steel, nickel and cobalt

4 Interaction with other magnets Repel from another magnet with like poles and attracts magnets with unlike poles

5 Identification Can only be identified by repulsion

(b) describe induced magnetism

Meaning of induced magnetism Mechanism of induced magnetism

Magnetic materials are magnetised temporarily when near or in contact with a permanent magnet

Magnetic field from the magnetic material aligns with the domains of the permanent magnet

(c) describe electrical methods of magnetisation and demagnetisation

Electrical magnetisation Electrical demagnetisation

• Magnetic object placed in a solenoid (a cylindrical coil of insulated copper wires carrying currents)

• Strong magnetic field produced when direct electric current, D.C., flows through the solenoid

• The magnetic field produced will magnetise the magnetic object

• Field is determined by right-hand grip rule:

• Magnet is inserted into a solenoid and an alternating current, A.C., flows through it

• When the magnet is withdrawn slowly from the coil, the magnet is constantly being magnetised in opposite directions by the alternating current

• The domains in the magnet will be arranged different directions, cancelling their magnetic effect

• Magnetic field around the solenoid causes the magnet to lose its magnetism

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Properties of magnetised objects Properties of demagnetised objects

• Have properties of a magnet

• Magnetic domains point in the same direction

• Do not have any properties of a magnet

• Magnetic domains point in random directions

• No resultant magnetic effect present

(d) draw the magnetic field pattern around a bar magnet and between the poles of two bar

magnets (e) describe the plotting of magnetic field lines with a compass

Examples of magnetic field patterns Method to draw magnetic field pattern

• The magnetic field pattern of a single permanent magnet is shown on the right

• Field lines travel from N to S outside the magnet

• Field lines travel from S to N through the magnet

• Place the bar magnet at centre of piece of paper so that its North pole faces north and its South pole faces south

• Place a compass near one pole of the magnet and mark with dots the positions of the North and South ends of the compass needle, labeling them Y and X respectively

• Move the compass such that the south end of the compass needle is exactly over Y

• Mark the new posltlon of the north end with a third dot labeled Z

• Repeat the above until the compass reaches the other pole of the bar magnet

• Join the series of dots with a curve and this will give a field line of the magnetic field

• Repeat for more field lines and indicate the direction of the lines

(f) distinguish between the properties and uses of temporary magnets (e.g. iron) and

permanent magnets (e.g. steel)

Differences Temporary magnets Permanent magnets

Example Magnetised iron Magnetised steel

Nature Soft magnetic material Hard magnetic material

Ease of magnetisation Easily magnetised Hard to magnetise

Retainment of magnetism Do not easily retain magnetism Easily retains magnetism

Uses • Electromagnet

• Transformer core

• Shielding

• Magnetic door catch

• Moving-coil ammeter

• Moving-coil loudspeaker

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21. Electromagnetism

Content

• Magnetic effect of a current

• Applications of the magnetic effect of a current

• Force on a current-carrying conductor

• The d.c. motor

Learning Outcomes


(a) draw the pattern of the magnetic field due to currents in straight wires and in solenoids

and state the effect on the magnetic field of changing the magnitude and/or direction of the

current

Scenario Patterns of magnetic field due to current

Current in solenoids

Case Clockwise Anti-clockwise

Front-view

• The arrows represent the direction of current

• A cross indicates magnetic field lines travelling inwards into the plane (away from you)

• The arrows represent the direction of current

• A dot indicates magnetic field lines travelling outwards from the plane (towards from you)

Representations of arrows and cross/dot can be interchanged (i.e. cross/dot can represent direction of current, arrows represent magnetic field)

Representations of arrows and cross/dot can be interchanged (i.e. cross/dot can represent direction of current, arrows represent magnetic field)

Side-view

Currents in straight wires

Case Current in the same direction Current in opposite directions

Magnetic field

Illustration

Remarks The most common rule used here is the right hand grip rule [which has been illustrated in learning outcome 20(c)]

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(b) describe the application of the magnetic effect of a current in a circuit breaker

Magnetic effect of current

• When current is increased to a high level, the solenoid of circuit breaker gains magnetism and becomes a strong electromagnet

• Stronger magnetic fields produce a force that enables the solenoid to attract iron armature connected in the circuit, breaking the circuit

When current is within the limit When there is a short circuit or overload

• The solenoid magnetic field is not strong enough to attract the soft iron latch

• The interrupt point remains closed and current flows normally through the circuit

• A sudden surge of current is present

• Solenoid gains magnetism and becomes a strong electromagnet due to larger current

• It is able to attract the soft iron latch and release the spring

• The safety bar is pushed outward

• The interrupt point opens and current is cut off

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(c) describe experiments to show the force on a current-carrying conductor, and on a beam

of charged particles, in a magnetic field, including the effect of reversing (i) the current (ii)

the direction of the field

Current-carrying conductor in magnetic field

Current-carrying conductor

Magnetic field from magnets

Explanation

• In this case, current that flows outwards in a straight line instead of in a solenoid will cause magnetic field lines to travel anti-clockwise

• Field lines at the top of the wire flow in the same direction as the magnetic field from the magnets

• On the other hand, field lines at the bottom of the wire flow in the opposite direction as the magnetic field from the magnets

Combined diagram Explanation Experimental setup

• As a result, when the conductor is placed in the magnetic field from the magnets, the magnetic field produced above the wire will be much stronger than the magnetic field produced below the wire

• The strong resultant magnetic field at the top causes a force to push the conductor downwards

Remarks

• The most common rule used here is Fleming’s left-hand rule [which will be illustrated in the next learning outcome]

• This rule is used only when current from a source causes a force to be produced

Beam of charged particles in magnetic field

Case Positive charge Negative charge

Force direction

A cross indicates magnetic field lines travelling inwards into the plane (away from you)

Remarks • The most common rule used here is Fleming’s left-hand rule [which will be illustrated in the next learning outcome]


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(d) deduce the relative directions of force, field and current when any two of these

quantities are at right angles to each other using Fleming’s left-hand rule

Fleming’s left-hand rule

Function Illustration using current-carrying conductor Legend

• The relative directions of force, field and currents for both a current-carrying conductor and a beam of charged particles illustrated above can be found using your left hand by Fleming’s left-hand rule


Finger Direction Symbol

1 Force F

2 Magnetic field

B

3 Current I

(e) describe the field patterns between currents in parallel conductors and relate these to

the forces which exist between the conductors (excluding the Earth’s field)

Differences Currents in parallel conductors

Case Current in the same direction Current in opposite directions

Magnetic field

Respective

Combined

Illustration

Explanation • The magnetic field lines in between the conductors (both currents travelling inwards) are in opposite directions, cancelling out each other

• This causes the magnetic field to be stronger in all other areas, pushing the conductors towards each other

• The magnetic field lines in between the conductors (currents in opposite directions) are in the same direction, which intensifies the magnetic field present there

• Since the magnetic field is now stronger in between the conductors than all the other areas, the conductors are pushed away from each other

F

B

I

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(f) explain how a current-carrying coil in a magnetic field experiences a turning effect and

that the effect is increased by increasing (i) the number of turns on the coil (ii) the current

Turning effect due to current-carrying coil in a magnetic field

Case Due to pivot Due to axis

Diagram

Explanation ▪ As current through the thick, stiff copper wire and magnetic field are perpendicular to each other,

▪ by Fleming’s left hand rule, ▪ a force is produced that pushes the wire

away from the powerful permanent magnet ▪ Since the bent stiff copper or brass wire

acts as a pivot, ▪ a perpendicular distance between the pivot

and the force is present,

▪ thus a clockwise turning effect is also produced

▪ As current through the coil and magnetic field are perpendicular to each other at both sides,

▪ by Fleming’s left hand rule, ▪ a force is produced ▪ The coil at the side nearer to the N pole is

pushed forward as current travels upwards ▪ whereas the coil at the side nearer to the

S pole is pushed backward as current as travels downwards

▪ This produces an anti-clockwise turning

effect about a central axis (dotted lines)

Increasing force of the turning effect

By increasing number of turns of coil By increasing current

• Each loop of wires produces its own magnetic field

• Since the magnetic field strength is the sum of the field lines,

• more lines will produce a stronger magnetic field and hence greater force

• A larger current will produce a greater concentration of field lines

• A strong field will lead to a larger force

(g) discuss how this turning effect is used in the action of an electric motor

Differences Uses of electrically produced turning effects

D.C. motors A.C. motors

Examples • Toy cars

• DVDs

• Hard disks

• Electric fans

• Hair dryers

• Washing machines

Reason Rotation in a fixed direction is required

Alternating rotation in the clockwise and anticlockwise directions is required

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(h) describe the action of a split-ring commutator in a two-pole, single-coil motor and the

effect of winding the coil on to a soft-iron cylinder

Split-ring commutator

Diagram Description

• Constant magnetic field by two permanent magnets interacts with the magnetic field in the U-shaped coil due to the direct current

• Based on Fleming’s left hand rule, the wires at each side of the coil experience an equal but opposite force

• The turning effect created by the two forces causes the coil to rotate continuously in the same direction


Main components Function of components

Two permanent magnets

• N and S poles of both magnets face each other

• Provides the magnetic field (B)

D.C. circuit Provides the direct current flow (I)

Pair of carbon brushes

• Maintains continuous contact between the stationary external D.C. circuit and the split-ring commutator, which is linked to the rotating coil

• Ensures that the circuit is never broken during rotation


• Placed between the coil and carbon brushes

• Reverses direction of current in the coil every half a turn by the coil

• Ensures the coil rotates in the same (clockwise) direction thoroughout (if it is a continuous ring commutator, the coil will rotate in alternate directions instead)

Soft-iron cylindrical core

Winding the coil on to a soft-iron cylindrical core concentrates the magnetic field, increasing magnetic field strength

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22. Electromagnetic Induction

Content

• Principles of electromagnetic induction

• The a.c. generator

• Use of cathode-ray oscilloscope

• The transformer

Learning Outcomes


(a) deduce from Faraday’s experiments on electromagnetic induction or other appropriate

experiments: (i) that a changing magnetic field can induce an e.m.f. in a circuit (ii) that the

direction of the induced e.m.f. opposes the change producing it

Electromagnetic induction

Laws Faraday’s law Lenz’s law

Definition ▪ E.m.f. generated in a conductor ▪ is proportional to the rate of

change of the magnetic lines of force linking with the circuit

▪ Direction of the induced e.m.f. ▪ and hence the induced current in a closed circuit ▪ is always such as to oppose the change in the

applied magnetic field

Principles Changing magnetic field can induce an e.m.f. in a circuit

Direction of the induced e.m.f. opposes the change producing it

Description of principle

▪ Changing magnetic field produces a continuously changing magnetic flux linking with the secondary solenoid

▪ Since Faraday’s law states e.m.f. generated in a conductor

▪ is proportional to the rate of change of the magnetic lines of force linking with the circuit,

▪ e.m.f. will be induced, producing a current that will allow power to be transmitted

▪ Since Lenz’s law states direction of the induced e.m.f.

▪ and hence the induced current in a closed circuit ▪ is always such as to oppose the change in the

applied magnetic field, ▪ the drawing in of a north pole of a magnet into a

solenoid ▪ (or drawing out of a south pole) ▪ will produce a north pole at the end of the solenoid

nearest to the magnet ▪ as the solenoid will repel the magnet, ▪ and vice versa

Experiments

Opposite direction of magnetic field

Opposite direction of magnetic field

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(iii) the factors affecting the magnitude of the induced e.m.f.

Factors to increase the magnitude of induced e.m.f.

Increased number of turns of coil

Increased strength of magnet

Increased speed of movement of magnet or coil

Addition of a soft iron core

▪ Increased number of turns of coil

▪ since more magnetic lines of force

▪ produce stronger magnetic field and hence greater force

▪ Increased strength of magnet

▪ will produce a stronger magnetic field

▪ and hence greater force

▪ Increased speed of movement of magnet or coil in displacement to each other

▪ will increase rate of change of magnetic field lines

▪ and frequency of the emf against time graph

▪ Addition of a soft iron core

▪ since it becomes a magnet within the field lines

▪ such that it increases the concentration of magnetic field lines

The above factors increase the rate of change of magnetic flux linking the circuit and hence emf by Faraday’s law

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(b) describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of

slip rings (where needed) (c) sketch a graph of voltage output against time for a simple a.c.

generator

A.C. generator [read ‘Remarks’ to understand Fleming’s right hand rule first]

Diagram of generator Diagram of electrical load Graph of induced e.m.f. / time

A.C. voltage from the generator may be received by an electrical load (e.g. light bulb) connected to it

Use of slip rings Description of action of A.C. generator

• Keeps the electrical load in a fixed position (instead of rotating continuously)

• Maintains continuous contact with the carbon brushes when the coil is rotating

• This ensures that the alternating current induced in the coil is transferred to the external circuit

• Electromagnetic device which transforms mechanical energy into electrical energy

• Coil is rotated (usually with a handle) about an axis between the two opposing poles of a permanent magnet

• When rectangular coil is parallel to the magnetic lines of force, both sides of the coil cuts through the magnetic field lines at the greatest rate, hence induced e.m.f. is maximum

• The next time rectangular coil becomes parallel to the magnetic lines of force, current will be reversed and thus induced e.m.f. will be minimum

• When rectangular coil is perpendicular to the magnetic lines of force, it is not cutting through the magnetic field lines

• The rate of change of magnetic lines of force at this instance is zero, hence no e.m.f. is induced

Remarks

• The most common rule used here is Fleming’s right-hand rule, which is used when the application of a force causes current to be produced

• This is as opposed to Fleming’s left-hand rule, which is used only when current from a source causes a force to be produced

Factors affecting graph of induced e.m.f. against time

Number of coils Strength of magnet Speed of rotation

When number of coils doubles, ▪ amplitude doubles, ▪ frequency doubles and ▪ wavelength halves

When strength of magnet doubles, ▪ only amplitude doubles

When speed of rotation doubles, ▪ only amplitude doubles

induced e.m.f. / mV

F B

I

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(d) describe the use of a cathode-ray oscilloscope (c.r.o.) to display waveforms and to

measure potential differences and short intervals of time (detailed circuits, structure and

operation of the c.r.o. are not required)

Cathode-ray oscilloscope

Diagram for understanding only Mechanism for understanding only

• The electron gun emits a cathode-ray (i.e. beam of electrons) through thermonic emission

• The electron beam then strikes the flourescent screen, forming a bright spot

• The deflection system of X and Y plates controls the position the electrons strike on the fluorescent screen

• It does so by varying the voltage across the X and/or Y plates

Uses Component required to function

Measure potential differences

Voltage to be measured is applied to the Y-plates via the Y-input terminals

Display waveforms of potential differences

• The voltage measured is displayed on the fluorescent screen

• Time-base is switched off to show a fixed voltage or the amplitude of varying voltage

• Time-base is switched on to check for varying voltage or its frequency and wavelength

Measure short time intervals

• The device used to measure short time intervals between occurrences (e.g. microphone, when a sound is received at intervals) transmits the information received into voltage

• The voltage display shown represents the short time intervals to be measured

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(e) interpret c.r.o. displays of waveforms, potential differences and time intervals to solve

related problems

Time base / Hz Y-gain / V

• Signals being measured will have a wide range of frequencies

• Adjusting the time base of input allows us to view the signals to a appropriate range on the screen

• The gain determines sensitivity of oscilloscope

• Adjusted to measure the voltage

Examples Example 1 Example 2 Example 3 Example 4

Input 2 V -4 V 20 V -20 V

Y-gain 1 V/div 2 V/div 5 V/div 5 V/div

Gain-input relationship

Line is produced 2/1 = 2 div above

Line is produced -4/2 = 2 div below

Normal sine curve 20/5 = 4 div

Inverted sine curve 20/5 = 4 div

A.C. Input Not A.C. (i.e. 0 Hz) Not A.C. (i.e. 0 Hz) 50 Hz 25 Hz

Time base 25 Hz 25 Hz 25 Hz 25 Hz

Cycles 0/25 = 0 Cycles 0/25 = 0 Cycles 50/25 = 2 Cycles 50/25 = 1 Cycle

Graph

Graph when time base is turned off

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(f) describe the structure and principle of operation of a simple iron-cored transformer as

used for voltage transformations

Simple iron-cored transformer

Structure Principle

• Primary coil is wound on one side of laminated soft iron core and secondary coil on the other side with different number of turns

• The lamination reduces heat loss due to eddy currents in the soft iron core

• Applied alternating voltage at primary coil sets up changing magnetic field passing through soft core to the secondary coil

• Since Faraday’s law states e.m.f. generated in a conductor is proportional to rate of change of magnetic lines of force linking with the circuit,

• alternating current at the secondary coil produces a changing magnetic field (based on the turns ratio) which induces e.m.f. by electromagnetic induction

(g) recall and apply the equations VP / VS = NP / NS and VPIP = VSIS to new situations or to

solve related problems (for an ideal transformer)

Term Equations

Turns ratio •

Primary input voltage Number of turns in primary coil

Secondary input voltage Number of turns in secondary coil=

• P P

S S

V N

V N=

Power for transformers of 100% efficiency

• Power Primary input voltage Current in primary coil=

Secondary input voltage Current in secondary coil=

• P P S SP V I V I= =

Power for transformers of less than 100% efficiency

• Secondary input voltage Current in secondary coil

Efficiency Primary input voltage Current in primary coil=

• EfficiencyS S P PV I V I=

(h) describe the energy loss in cables and deduce the advantages of high voltage

transmission

Energy loss in cables Advantages of high voltage transmission

• Energy loss is due to Joule heating as the product of time, square of current flow and resistance of cables

• A decrease of either current flow or resistance of cables or both will decrease energy loss

• Having increased voltage will reduce current flow but increase insulation costs

• Having thick cables will reduce resistance but increase construction costs

• As output power is the product of voltage and current, increased voltage will reduce current flow greatly

• Since Joule heating is the product of the square of current flow and resistance of cables

• Power loss in the form of heat is thus decreased, allowing more power to be transmitted to households

-End-

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