120 Essential Concepts in Physics-Ans

8/10/2019 120 Essential Concepts in Physics-Ans

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120 Essential Concepts in Science

(Physics)!

1. Scalar Quantities are quantities that have magnitudeonly.

2. Vector quantities are quantities that have both magnitudeand direction.

3. To add up 2 vectors that acts outwards from the

same point, the parallelogramlaw can be used.

. To add up 2 vectors that are continuous in direction,

the trianglelaw can be used.

!. Speed is the rate of chan"e of distance.

#. Velocity is the rate of chan"e of displacement / distance

in a particular direction.

$. %cceleration is the rate of chan"e of velocity.

&. The "radient of a distance'time

"raph "ives the speed.

(. The area under a speed'time "raph "ives the

distance travelledwhile its "radient "ives the

acceleration.

1). *hen an ob+ect is dropped near the earth, itsaccelerationis constant at

10ms2if there is no air resistance.

11. *hen the forces actin" on a body are unbalanced, it will e-perience a

resultant force and it will acceleratebecause / ma.

1

distance / m

time / s

100

8020 120

150

50

1006040

200

speed/ m/s

time / s

8

4010 60

12

4

503020

16


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12. *hen the forces actin" on a body are balanced, the resultant force actin"

on it is zeroand the body will either stay at rest / remain stationaryor

move with constant velocity.

13. riction causes surfaces to heatup and results in wear and tear. 0t also

reduceseciency in machinery.

1. ass is the amount of matterin a body.

1!. *ei"ht is the gravitational force actin" on the body.

1#. Massis constant whereas weightdepends on the "ravitational eld

stren"th of the location.

1$. *ei"ht is measured in Newton4unit5 usin" a spring balance.

1&. ass is measured in kilogram4unit5 usin" a beam balance.

1(. Massis a scalar whereas weightis a vector.

2). 0nertia is the reluctanceof a body to chan"e its state of restor motion.

21. 6ensity is the massper unit volume.

22. 7ravitational eld is a regionin which a body e-periences gravitational

force.

23. 7ravitational eld stren"th is the gravitationalforce actin" on a unit

mass.

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2. oment is the turning eectof a force.

2!. 8rinciple of moment states that when an ob+ect is in euilibrium!the sum

of its clockwise momentabout any point is equal to the sum of

itsanticlockwise momentabout the same point.

2#. % stable ob+ect has wide base areaand low centre of gravity.

2$. 8ressure is the force actin" on a unit area.

2&. % force actin" on a small contact area "ives rise to a large

pressure.

2(. 9onservation of ener"y states that ener"y cannot be createdor

destroyedbut it can be converted / transferred from one form to

another.

3). To increase the "ravitational potential ener"y of a body, we need to

increase its height above the ground.

31. To increase the :inetic ener"y of a body, we need to increase itsspeed.

32. *hen a movin" ob+ect is stopped by friction, its kineticener"y is

converted to thermalener"y.

33. *hen an ob+ect falls from a hei"ht, it "ained kinetic ener"y while losin"

gravitational potentialener"y.

3. 8ower is the rate of work done.

3!. Solids have -ed volumeand shapeand

it cannot be compressed.

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3#. ;iquids have -ed volumebut its shapeis not -ed. 0t is not easy /

di"cultto compress and it assumes the shapeof its container.

3$. 7ases< volume and shape are not #$edand it is hi"hly compressible.

3&. Solid particles are closely /tightlypac:edin a regular / orderlypattern. They

vibrate in their -ed position. They have

stron" intermolecularbondsbetween one

another.

3(. ;iquid particles are arran"ed randomly /

freelyand they are closeto one another. They vibrateand moveamon"

one another. Their intermolecular forces are strong.

). 7as particles are spaced far apartand they move randomlywith a fast /

highspeed. Their intermolecular forces are negligible / very weak.

1. *hen solid particles are heated, they will vibrate more vigorously, whenliquid or

"as particles are heated, they will movefaster.

2. Thermal ener"y is transferred from a re"ion of high

temperatureto a re"ion of low temperature.

3. *hen a solid is heated, the particles "ain energy

and vibratemore vi"orously. They collide with their less ener"etic

neighboursand transfer ener"y to them. This transfer of ener"y from one

particle to another by vibration is called conduction.


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. etals are "ood conductorsof heat while liuid / wood / plastic/

wool /%tyrofoamand still &trapped' airare very "ood insulators of

heat.

!. *hen a =uid 4liquid or "as5 is heated, it will e$pandand

become less denseThe hot =uid will rise to the top.

The cooler =uid at the top will sinkto ta:e its place

because it is denserThis circulation of =uid is :nown as

convection current and it will ensure that the =uid is

evenly heated.

#. 9onduction and convection cannot occur in vacuum.

$. >adiation is the transfer of heat by infrared wave.

&. >adiation does not require a medium and is able to travel throu"h

vacuum.

(. % "ood absorber of heat is a goodemitter of heat.

!). >ate of radiation depends on the te$ture, colour , area

and temperatureof the surface.

!1. ?lac: and rou"h surfaces are good in emittin" absorbin" heat while

white and shiny surfaces are poorin emittin" absorbin" heat.

!2. *hen an ob+ect is heated, its

temperature increases because its

kinetic / internalener"y increases.

!3. eltin" is the process in which solidchan"es into liuidat the melting

point.Solidication is the process in which liuidchan"es into solidat

the freezing point.

!. The heatin" curve shows how temperature

varies when a substance is heated. %t V*, it

!


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is in the solidstate. %t *@, solidand liuidstates are in equilibrium as

the substance under"oes the meltingprocess. %t AB, it under"oes

boilingprocess whereby liuidchan"es into gas. Cner"y is absorbed

from V to B but temperature does not chan"e durin" the chan"e of state

because it is used to brea: intermolecular bonds.

!!. Cvaporation and boilingare similar because both

involve chan"in" a liuidinto a gas.

!#. ?oilin" ta:es place at a -ed temperature whereas

evaporation ta:es place at any temperature below

boiling point.

!$. % wave transfers energy by vibration. Do matteris transferred when a

wave moves.

!&. Transverse waves are waves that travelin a

direction that is perpendicular to the

direction of vibration of the particles in the

medium.

!(. ;on"itudinal waves are waves that travel

parallelto the directionof vibration of the

particles in the medium.

#). %n e-ample of lon"itudinal wave is sound wavewhile water waveis an

e-ample of transverse wave.

#1. %mplitude of a wave is the ma$imum

dispalcement of the particles in the

medium.

#2. requency is the number of complete wave"enerated in 1s.

#


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#3. 8eriod of a wave is the time ta:en to generate a complete wave.

#. *avelen"th is the distance between 2 particles that are in phase / (

crests / ( troughs.

#!. Speed of the wave is the distance traveled by the wavein 1 s.

##. *avefront is an ima"inary line that +oins all theparticles that are in

phase in a wave.

#$. Sound is produced by the vibrationof ob+ects.

#&. *hen an ob+ect vibrates, it alternates between pushin" the air layers

to"ether to cause a re"ion of compressionand pullin" the air layers

apart to cause a re"ion of rarefactionThe air layers continues to vibrate

parallelto the direction of the sound wave to propa"ate the sound wave.

#(. Sound cannot travel in vacuum.

$). Sound travel fastest in solid and slowest in gas.

$1. *hen sound is re)ectedecho is formed.

$2. % sound wave with a lar"e amplitude is louder than a sound with a

smaller amplitude.

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$3. The hi"her the frequency of the sound wave, the higherthe pitch of the

sound.

$. *hen li"ht ray "ets re=ected, its an"le of incidence

is equal to its an"le of re)ection.

$!. *hen li"ht enters a diEerent medium, it bends /

gets refractedbecause its speedchan"es.

$#. ;i"ht will bend towards the normal when it enters a

densermedium and bend away from the normal

when it enters a less densemedium.

$$. >efractive inde- of a medium is the ratio of the speed of li"ht in vacuum

and in the medium.

$&. 9ritical an"le is the an"le of incidencein

the densermedium when the an"le of

refractionis ()o.

$(. *hen the an"le of incidence in the denser

medium is less than critical an"le, li"ht will

be refractedout of the medium.

&). *hen the an"le of incidence in the denser medium is more than the

critical an"le, total internal re)ectionwill occur.

&1. ocal len"th of a lens is the distance between its

optical centreand principal focus.

&


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&2. 0n order to use a conver"in" lens as a ma"nifyin" "lass, the ob+ect must be

placed at a distance lessthan the focal len"th. The ima"e obtained will be

virtualbecause it cannot be captured on a screen.

&3. *hen an ob+ect is placed at a distanceequal to the focal lengthof the lens, no

ima"e is formed as parallel li"ht rays

emer"ed from the lens.

&. % real and inverted ima"e will be obtained

when the ob+ect is placed furtherthan the

focal len"th from the lens.

&!. To obtain a real, inverted ima"e that is of the same siFe as the ob+ect, it

needs to be placed at a distance equal tothe( times the focal length

from the lens.

. Cvery wave in the electroma"netic spectrum is transverse in nature and

they travel with the same speed of * $ 10+m/sin vacuum.

&$. 7amma wave has the lar"est freuencyand the smallest wavelengthin

the electroma"netic spectrum.

&&. There are 2 :inds of char"es, positivechar"es and negativechar"es.9har"es are measured in ,oulombs4unit5.

(


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&(. -nlikechar"es attract and likechar"es repel.

(). Clectric ield lines of a positive and ne"ative char"e.

(1. Clectric eld lines between 4i5 2 li:e and 4ii5 2 unli:e char"es.

4i5

4ii5

(2. 9urrent is the rate of )ow of charges.0t is

measured with an ammeter that is connected in seriesto the circuit.

(3. Clectrons =ow in the oppositedirection as the conventional current.

(. Clectromotive force 4C5 is the wor: done by an electricalsourceto

drive 1 ,of char"e around the complete circuit.

(!. The potential diEerence across a component is the energy neededto

drive 1 9 of char"e throu"h the component. 0t is measured with a

voltmeter connected in parallelacross the component.

(#. >esistance is dened as the ratio of potential dierenceand current.

($. *hen the len"th of a wire is doubled, its resistance isdoubled.*hen the

cross'sectional area of a wire is doubled its resistance is halved

(&. 0n a series circuit,

1)

G


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the currentat every point is the same

the sum of the potential dierenceis equal to the C of the source

the eEective resistance is the sum of the resistance in the circuit.

((. 0n a parallel circuit,

the sum of the current that entersa point is equal to the sum of thecurrent that leavesthe same point,

the potential diEerence across the separate branches is the same

the eEective resistance can be obtained by the formula

1 1 1 (

1)).uses are used to prevent e$cessive current / current larger than its

rating from enterin" the circuit.

1)1.Carth wire prevents electric shockto the user when heaccidentally touches the metalcasin" of an appliance that has

become liveaccidentally.

1)2.*hen the metal casin" of an appliance becomes live accidentally, current

will start to =ow to the earth throu"h the earth wire. Since the resistance

of the earth wire is small!the current will be very large. That will blow the

fuseand isolate the faulty appliance.

11

'1

>C/

>C/ >1G >2


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1)3.The fuse and switch must be connected to the livewire so that the

appliance will be isolated from highpotential when the fuse blow or when

the switch is closed.

1).The earth wire is yellow and green in colour, the neutral wire is bluein

colour and the live wire is brownin colour.

1)!.The neutralwire and earthwire are at Fero potential 4) V5 while the live

wire is at potential that is much hi"her or lower than the neutral wire to

provide a potential diEerence for current to =ow.

1)#. 0f the casin" of an appliance is made of an insulator, it is said to be

doubleinsulated.

1)$.;i:e poles of a ma"net repelwhile unli:e poles attract.

1)&.% freely suspended ma"net will always point in the

northsouthdirection.

1)(. 0nduced ma"netism is the ma"netism produced in a soft

iron when a magnetis brou"ht near it.

11).To ma"netise a ma"netic material, it is put in a solenoid

and a direct currentis passed throu"h the solenoid. To

determine the polarity of the ma"net, the right hand

grip rule is used.

111. To dema"netiFe a ma"net, it is put in a solenoid

and an alternating current &ac'is passed

throu"h the solenoid and the ma"net is pulled

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out of the solenoid slowly as the current is still

=owin".

112.The ma"netic eld of a bar ma"net

113.The ma"netic eld between 4i5 2 li:e poles 4ii5 2 unli:e poles of ma"nets

4i5

4ii5

11.0ron is easily ma"netised and dema"netiFed. Hence it is used as an

electro temporaryma"net.

11!.Steel is di"cultto ma"netise and dema"netiFe. Hence it is used as a

permanentma"net.

11#.The compass needle is made of permanentma"net while the electric bell

is an e-ample of the application of temporary / electroma"net.

11$.*hen current =ows throu"h a conductor, it produces a magneticeld.

11&.a"netic eld of current =owin" into 4i5 and out of the 4ii5 pa"e

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11(.% current' carryin" conductor

e-periences a force when placed in a

magneticeld. The directionof the force can be determined by the

lemin"

120 Essential Concepts in Physics-Ans

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