Physics Module Form 5 GCKL 2010 - KS Thong's Blog | PHYSICS · PDF file · 2012-02-012012-02-01 · Physics Module Form 5 chapter 1 : Waves GCKL 2011 1-2 5. In the...

. Physics Module Form 5 chapter 1 : Waves GCKL 2011

1-1

U N D E R S T A N D I N G W A V E S

What is meant by a wavefront An imaginary line that joins all the points on the crest of a wave.

State the direction of propagation of

waves in relation to wavefronts The direction of propagation of a wave is perpendicular to its

wavefront.

What is transverse wave? A transverse wave is a wave in which particles of the medium

oscillate in the direction of the propagation of the waves.

Water waves and electromagnetic waves are examples of

this type of waves.

What is longitudinal wave?

A longitudinal wave is a wave which the particles of the medium

oscillate in the direction parallel to the direction in which the

wave moves

Sound waves is the example of this type of waves.

Fill in the blank with the correct answer given below

frequency period Hertz ( Hz) amplitude

1. The amplitude of an oscillation is the maximum displacement for one complete

oscillation .

2. The period of the oscillation is the time taken to complete one oscillation.

3. The frequency of the oscillation is the number of complete oscillation made in one

second. The SI unit is Hertz ( Hz)

Label the graph below and fill in the blank with correct answer.

4. In the displacement – time graph as shown above, amplitude is represented by the symbol

of a and period is represented by the symbol of T

1.1

Displacement – time graph


1-2

5. In the displacement – distance graph as shown above, amplitude is represented by the symbol of

a and wavelength is represented by the symbol of λ

6. Damping is occur when in an oscillating system when the system loses ( gain /

loses) energy to surrounding in the form of heat ( heat / chemical ) energy.

7. The force responsible for damping is called dissipative ( equilibrium / dissipative) forces.

8. In a simple pendulum, its natural frequency depending on its length ( length /

mass ).

9. When an oscillating systems driven at its natural frequency, the system is said to be at

reasonance ( damping / reasonance)

10. A wave travels with a speed of 3.0 x 108 ms

-1

(a) What is the frequency of the wave if its wave length is 1.0 m?

(b) Another wave is travelling with the same speed but has a frequency of 1.5 x 1012

Hz.

What is the wavelength of the wave?

Solution.

(a) f = 3.0 x 108 (b) λ = v / f

1.0 = 3.0 x 108

1.5 x 1012

= 3.0 x 108 Hz = 2.0 x 10

-4 m

Displacement – distance graph

Wave speed , v = f λ


1-3

S/c

m

2 4 6 l/cm

S/cm

t/s

2 4 6

11. The displacement – time graphs and displacement – distance graph describe the motion of a

particular wave. Determine the speed of the wave.

a) Displacement – time graph (b) Displacement – distance graph

solution :

v = f λ, f = 1 / T

from (a) : T = 4 s, from (b) : λ = 4 cm

f = 0.25 Hz

v = f λ

= 0.25 x 4

= 1 cm s-1

12.

Based in the displacement-distance graph of a wave, find

(a) the amplitude (b) the wavelength of the wave

( ans : 5 cm) ( ans : 2 cm)

13. Calculate the frequency of the given wave below

f = 1/T

= 1 / 4

= 0.25 Hz.

Displacement/cm

Distance/cm

1 2

5

-5

3


1-4

Practise 1.1

1.

Diagram 1.11

Base on the diagram 1.11 above, which

distance represents the amplitude?

2. Diagram 1.12 shows how displacement

how varies with time.

Diagram 1.12

Which of the following is true?

Amplitude/ m Period / s Frequency / Hz

A 0 .1 0.50 2

B 0.2 0.50 1

4. The period of oscillations of a simple

pendulum increases when the

________________________ increases.

A length of the pendulum

B mass of the bob of the pendulum

C acceleration due to gravity

5. Diagram 1.14 shows a wavefront pattern produces by a dipper vibrating at a frequency of 12 Hz in a ripple tank.

Diagram 1.14 What is the speed of the waves? A. 2 cms

-1 B. 8 cms

-1

C. 12 cms-1

D. 18 cms-1

E. 36 cms-1

C 0.1 0.25 4

D 0.2 0.50 2

3. Diagram 1.13 shows the displacement-

time graph of an oscillating system

Diagram 1.13

The system which produces this graph is

having

A. a perpertual oscillation B. a forced oscillation C. a damped oscillation D. a resonance

9. Diagram 1.15 shows the cross section of

water waves.

Diagram 1.15

Which of the following statements is true

about the water waves?

A. T and U have the same phase

B. Wave energy is transferred from position

S to U.

C. The wave length is the distance between S

and U

D. The particles at U oscillates in a direction

parallel to the direction of the wave

propagation


1-5

10. The graphs show the cross-sections of water waves. Which wave has the greatest energy?

11. Which graph represents a wave with

amplitude of 4.0 cm and period of 0.05 s

11. Diagram 1.16 shows the displacement distance

graph. The frequency of the wave is 5.0 Hz.

What is the velocity of the wave?

A. 50 cms-1

C. 100 cms-1

B. 75 cms-1

D. 150 cms-1

11. Diagram 1.16 shows a silky spring being

moved left and right continuously.

Diagram 1.16

(a) Complete the sentence below by ticking

(√) the correct box.

The wave produced by the slinky spring

is a

Transverse wave

Longitudinal wave

b). On diagram 1.16. mark ‘ X’ on any of the

crest of the wave.

c) Complete the following sentence by

underlining the correct phase in the bracket.

d) What is transferred by the wave?

Energy

√


1-6

1.2 ANALYSING REFLECTION OF WAVES.

1. complete the diagram 1.21 below to show the reflected waves.

Diagram 1.21

2. Fill in the box with the correct answer.

3. Draw the correct pattern of reflected water waves.

wavefronts

(a)

reflector

wavefronts

(b)

reflector

Incidence ray

Reflected ray

i = incidence angle

r = reflected angle

1.2


1-7

(c)

(c) Compare the following quantities before and after reflection.

(i) velocity: ____remain the same__________

(ii) frequency:_ ____remain the same__________

(iii) wavelength: ____remain the same__________

(iv) direction:_____ changes after undergoing reflection.

d) In reflection , the angle of reflection is always equal to angle of reflection

Incident light ray

Reflected light ray


1-8

Practice 1.2

1. Which of the following characteristic of waves changes when the wave are reflected?

A. Direction of propagation

B. Wavelength

C. Frequency

D. Speed

2. What happens to the wave length and the magnitude of the velocity of water waves when it is

reflected?

3. Diagram 1.22 shows a sound wave reflected from a concrete wall.

Which statement is correct about the reflected and incident waves?

A. The speed of the reflected waves is the same as the speed of the incident waves.

B. The wavelength of the reflected waves is shorter than that of the incident waves.

C. The frequency of the reflected waves is lower than that of the incident waves.

D. The directions of the reflected waves are always at right angles to the incident waves.

4. Echo is a phenomenon caused by

A the refraction of sound waves

B the reflection of sound waves

C the diffraction of sound waves

D the polarization of sound waves

5 Diagram 1.23 shows the wavefront of a plane wave wave incident on a plane reflector.

Which comparison is correct about the reflected sound wave and the incident sound wave?

A. The wavelength of the incident wave is shorter than the reflected wave.

B. The speed of the incident wave and the reflected wave is the same.

C. The frequency of the incident wave is less than the reflected wave.

D. The angle of incident wave is greater than the angle of reflection of the reflected wave.

Wavelength Magnitude of velocity

A. Unchanged Unchanged

B. Increases Decreases

C. Decreases Increases

D. Increases unchanged

Diagram 1.23

Diagram 1.22


1-9

6. Diagram 1.24 show the apparatus is used to investigate the reflection of sound waves. At

what position of the cardboard tube is adjusted until a loud ticking sound of the stop watch is

heard?

7. Diagram 1.25 and Diagram 1.26 show the water and sound waves propagating towards a

reflector.

ii) With reference to Diagram 1.25 and Diagram 1.26 , compare the incident and reflected angle,

wavelength, frequency, speed and direction of propagation of the reflected

Incident angle in diagram 1.25 and 1.26 is equal to reflected angle, the wavelength in diagram 1.25

and diagram 1.26 remain the same, frequency of diagram 1.25 and 1.26 remain the same, speed of

diagram 1.25 and 1.26 remain the same and direction of propagation of direction of propagation of

diagram 1.25 and diagram 1.26 is changing.

Norm

al Ll Direction of reflected

waves

wave

Reflect

edwave

front

Incident

wavefro

nts

Diagram 1.25

i

r

E

ar

Stop watch

Card

board

tube

Har

d

surf

ace

Diagram 1.26

Diagram 1.24


1-10

Analysing refraction of waves.

Describe

refraction of

waves in terms

of the angle of

incidence, angle

of refraction,

wavelength,

frequency, speed

and direction of

propagation

1. Waves can be refracted as they move from one medium ( volume /

medium) to another.

2. When water waves travel from one area to another area of different depth, their

speed changes ( remain / changes ) and the frequency remain (remain /

changes) .

3. The wavelength of waves in deep area is longer ( shorter / longer ) than that in

the shallow area.

4. When waves travel from a denser medium to less dense medium , they refracted

towards (away / towards) to normal.

Diagram 1.30

5. Diagram 1.30 shows the incident ray is refracted ... towards ( away / towards ) to

normal.

Draw a diagram

to show

refraction of

wave

Complete the diagrams below.

1.3


1-11

Why is the wave

bend according

to the shape of

the shoreline

when they are

approaching the

beach?

Diagram 1.31: the shape of shoreline when they are approaching the beach

uniform speed depth of the sea parallel shallower

reduce refraction refracted wavefront

towards

In the centre of the ocean, the water wave travel at uniform

speed as the depth of the sea water is uniform. Hence the wavefront are straight and

parallel to each other.

When the waves reach the coast, the water is shallower . Wave speed is reduce

and refraction occurs. The wavefront are refracted and become closer to

each other.

Refraction causes the wavefront to be bent towards the normal and this results

the wavefront following the shape of the coastline.

Figure 1.32 Figure 1.33

Why sound can be heard over a longer distance on a cold night compared

with a hot day as illustrated in diagram 1.32 and 1.33

Sound wave travel faster in warm air ( warm air / cool air) than in cool air ( warm air / cool air). On

hot day, the hot surface of the earth causes layer of air ( layer of air/ layer of density) near the

surface to be warmer ( colder / warmer). This causes sound waves ( light waves / sound waves)

to be refracted away ( away / closer) from the earth. During night time, the sound waves travel

slower ( slower / faster ) in the cooler layer of air near ( near / upper ) the surface of the earth than

in the upper ( near / upper ) warmer air. As a result , the wave are refracted (refracted / reflected)

towards the earth. This explain why sound can be heard over a longer distance on a cold night

compared with a hot day.


1-12

Practice 1.3

1. Diagram 1.34 shows water waves

propagating through a Perspex block in a

ripple tank.

Diagram 1.4

Which wave pattern is observed when the

waves pass through the perspex bloc.

2. Diagram 1.35 shows water waves

propagating in an area of different depths.

Diagram 1.35

Which of the following diagrams shows the

propagation of the waves correctly?

3. When water waves pass from deep water into

shallow water, how do the speed,

wavelength and frequency change?

Speed Wavelength Frequency

A Increases Decreases No change

B Decreases Increases Decreases

C Increases Increases No change

D Decreases Decreases No change

4. An observer cannot see the coin in an empty

glass as shown in figure (a). However he can

see the coin when the glass is filled with

water as shown in figure (b)

Figure (a) Figure (b)

The observer can see the coin in Figure (b) due to

A the total internal reflection of light

B the refraction of light

C the reflection of light

D the diffraction of light

4. A tilted basin contains water. Water is

dripped at a constant rate into the basin as

shown in the diagram below.

Which pattern of the wavefronts will be

observed in the basin?


1-13

5. A ray of light passes from water to air.

Which labeled arrow shows the direction of

the ray in air?

6. Diagram 1.36 shows the side view of two

ripple tanks. When the motors are switched

on, water waves with the same frequency are

produced,

Diagram 1.36

Diagram 1.37 shows the waves formed on

the screens.

Diagram 1.37

a) What is the meaning of frequency?

Number of complete oscillations in one

second

b) Observe diagram 1.36 and diagram 1.37.

(i) compare the depths of the water in region X

and region Y.

The depth of region X is greater than in

region Y.

(ii) Compare the wavelength of the waves in

region X and region Y.

Wavelength of the waves in region X is

longer than region Y.

(iii) Relate the depth of water to the wave length

of the waves.

The deeper the water, the longer the

wavelength.

(iv) Name the wave phenomenon involved.

Refraction.

c) Explain why the wave front of the sea will

follow the shape of the shore when it

approaches the shore.

In the ocean, wavefronts are straight and

parallel as the wave speed is uniform.

When a wave moves towards the shore, the

depth of the sea water decreases, the

velocity of the water decreases.

Refraction occur and the sea water

refracted towards the normal. This causes

the wavefront follow the shape of the

shore.

7. Diagram 1.38 (a) shows the wave formed

without a flat piece of plastic and diagram

1.38 (b) shoes the wave with a flat piece of

plastic.

Diagram 1.38(a) Diagram 1.38(b)

a) Observe the diagram and state the difference

between diagram (a) and diagram (b).

The wavelength of diagram1.38 (a) is

uniform while wavelength in diagram

1.38(b) is shorter when passes through the

plastic .

b) Using your answer, state the relationship

between depth and wavelength

The deeper the .water, the longer the

wavelength

c) Name the wave phenomenon involve

Refraction .


1-14

ANALYSING DIFFRACTION OF WAVES.

Describe

diffraction of

waves in terms

of wavelength,

frequency,

speed, direction

of propagation

and shape of

waves

1. Diffraction is the spreading out of waves when they move through a gap or

around an obstacle.

2. The narrower the gap, the more the wave spread out.

3. When the width of the gap is approximately the size of the wave length of the waves,

the diffracted waves spread out more.

4. When the gap is much wider than the wavelength of the wave, the diffraction is little.

5. After diffraction, the frequency remain unchange, the wavelength remain

unchange, and the speed remain unchange,

6. The direction of propagation of the diffracted waves changes.

Draw a diagram

to show

diffraction of

waves

Complete the diagrams below.

1.4


1-15

Practice 1.4

1. Which of the following figure is true to

show the diffraction of a water wave?

2. Diagram 1.40 shows the bright and dark

bands of the wave patterns formed on the

screen when plane waves pass through

narrow and wide gaps.

Diagram 1.40

a) Observe Figure 1.40 compare the waves

pattern and the wavelength of the waves

after they pass through the gaps.

The wave pattern after passing

through the gaps for narrow gap

formed circular waves and for wide

gap formed plane wave

The wavelength after pass through the

gap remain the same for narrow and

wide gap.

b) Relate the size of the gaps, the waves

patterns and the wavelengths to deduce a

relevant physics concept.

Narrow gap produced circular wave

while wider gap produced plane wave

and the wavelength remain the same.

3. Diagram 1.42 shows waves moving

towards a harbour.

Diagram 1.42

a) (i) What is the meaning of diffraction?

The spreading or bending of waves

around an obstacle or small opening.

(ii) Draw the wave pattern of the waves

after passing through the entrance of the

harbour.

b) The entrance is made wider to allow

more ships to enter harbour. What is

the effect on

(i) The wave passing through the

entrance?

Less diffraction / spreading

(ii) The harbour?

More damage to the harbour


1-16

ANALYSING INTERFERENCE OF WAVES

State the

principle of

superposition.

The principle of superposition state when two waves overlap, the resultant

displacement is equal to the sum of the displacements of the individual wave.

complete the diagram below.

Constructive interference occur when a wave peak meets a wave peak.

Destructive interference. occur when a wave peak meets a wave trough.

.

1.5

2a


1-17

Complete the diagram 1.51 below with the information given.

Diagram 1.51

a. Label P at a point of constructive interference.

b. Label Q at a point of destructive interference.

c. Draw the antinodal line and label it as R.

d. Draw the nodal line and label it as S.

5. In constructive interference, the resultant wave is at maximum amplitude.

6. In destructive interference, the resultant wave is at minimun amplitude.

7. An antinodes line is a line joining all the points where constructive interference takes place.

8. An nodes line is a line joining all the points where destructive interference takes place.

Diagram 1.52 Diagram 1.53

Node line

Node line Node

line Node

line

P

R

Q

S


1-18

Question 9,10 and 11 based on diagram 1.52 and diagram 1.53.

9. The distance between consecutive antinodal lines ; x , in diagram 1.52 is shorter compare to

diagram 1.53

10. The distance of between two coherent source; a, in diagram 1.52 is longer compare to

diagram 1.53.

11. When the x is shorter ( longer / shorter ) , the a is longer ( longer/ shorter.

12. The light interference experiment is also known as Young’s double – slit experiment. .

13. Diagram 1.54 show the interference pattern of a light wave.

Diagram 1.54

Bright fringes in diagram 1.54 correspond to constructive interference

Dark fringes in diagram 1.54 correspond to destructive interference

14. In the experiment set-up for the interference of sound wave, two loud speaker are connected to

the common audio signal generator to produce coherent source

15. Diagram 1.55 show two loud speakers placed apart from each other. A person hears alternating

loud and soft sounds as he walks along XY.

Diagram 1.55

The alternating loud and soft sounds is caused by interference of the sound waves, wher the loud

sound corresponds to the constructive interference and the soft sound corresponds to the

destructive interference

Interference pattern


1-19

λ = ax

D

λ = wavelength,

a = distance between two coherent source

x = distance between two consercutive nodes ( or antinodes)

D = perpendicular distance from the source and the position where x is measured.

Worked example.

In a Young’s double-slit experiment, a light of wavelength 633 nm passes through two slits which are

0.5 mm apart. Vertical fringes are observed on a screen placed 4 m from the slits.

a) Calculate the distance between two adjacent bright fringes.

Solution;

Answer : 5.1 mm

Two loudspeakers placed 2 m apart are connected to an audio signal generator that

is adjusted to produce sound wave of frequency 550 Hz. The figure shows the detection of loud and

soft sound as a person moves along a line, 4.0 m from the loud speakers.

Calculate the :

(a) Wavelength ( ans : 0.6 m) information :

(b) Speed ( ans : 330 m s-1

) a = 2 m, D = 4.0 m,

of the sound wave. x = 4.8 / 4 = 1.2 m

f = 550 Hz

Solution :

(a) λ = ax /D b) v = f λ,

= 2 x 1.2 = 550 x 0.6

= 0.6 m = 330 m s-1

º

º

º

º

Loud sound

º Soft sound

2.0 m

4.0 m

4.8 m


1-20

1. Diagram 1.56 shows the interference pattern

for water waves from two coherent source,

S1 and S2.

Diagram 1.56

Which of the following shows the

superposition of the waves at point Y?

2. In which diagram will destructive

interference occur when the wave meet?

3. Diagram 1.57 shows two coherent wave

propagate towards each other.

Diagram 1.57

Which diagram is correct when both waves

meet?

4. Diagram1.54 shows two loudspeakers

connected to an audio generator. Students

are standing at position where loud sounds

can be heard.

Diagram 1.54

(a) What type of wave is the sound waves?

Longitudinal wave

(b) Why are loud sounds heard by the students at

that positions?

Constructive interference takes place

(c) The distance between the two loudspeakers is

1.5 m. At 10.0 m from the loudspeakers, the

distance between two adjacent rows of student

is 4.0 m.

Calculate the wavelength of this sound wave.

λ = ax /D

= 1.5 x 4 = 0.6 m

10

A

C


1-21

5. Diagram 1.43 shows another modification to

the harbour to overcome the heavy sea

traffic problem. The wave pattern produced

at the entrances is shown in diagram 1.43

Diagram 1.43

(i) The wave pattern formed is caused by the

superposition of waves from two coherent

sources. What is the meaning of coherent

sources?

Source that produded wave of the same

freqyency and that in the same phase

(ii) Describe a movement of two similar ship

that are located at A and B.

Explain your answer

Ship at location A moves up and down

with high amplitude

Constructive interference occurs at A.

The ship at B remain calm.

Destructive interference occurs at B.

6. Diagram 1.43 shows the arrangement of

apparatus for Young’s double slit. A white

light source is passed through a coloured

filter to produce a monochromatic light.

Diagram 1.44 shows the pattern of the

fringe formed on the screen when a red

filter is used

The experiment is repeated by using a blue

filter and the fringes formed are shown in

diagram 1.45

.

White light source Single slit

Coloured

filter

White

screen

Double slit

Diagram 1.43

Diagram 1.45

Diagram 1.44

a) What is meant by monochromatic light?

Light with only one colour

b) Using the pattern of the fringes in figure

1.44 and 1.45, state two observation about

the distance between consecutive fringes

for the red light and blue light.

The distance between two consecutive

fringes for the same light is equal.

The distance between two consecutive

fringes for red light is longet than blue light.

c) Compare the wavelengths of red light to

blue light

The wavelengths of red light is longer

compare to blue light.

d) Compare the wavelengths of red light and

blue light with the distances between

consecutive fringes in (b)

The greater the wavelengths the greater the

distance between consecutive fringes.


1-22

ANALYSING SOUND WAVES

Describe sound

waves Sound waves are produced by vibration.

Sound waves are .longitudinal waves. ( tranverse wave s/ longitudinal waves).

Sound cannot be transmitted through a vacuum..

Loudness of a sound is dependent on its amplitude

The louder the sound, the bigger the amplitude

The pitch of a sound heard depends on the frequency

The higher the pitch of the sound, the higher the frequency.

1. Sound with frequency lower than 20 Hz is called infrasound

2. Sound with frequency higher than 20 000 Hz is called ultrasound.

3. Depth of the sea can be determine by using ultrasonic wave . The wave is sent by

from the boat to the seabed. are detected by hydrophone next to

the transmitter. The time is measured and the depth will be calculated.

Depth of sea , d = v x

Worked example

In an expedition to determine the depth of a freshwater lake using an ultrasonic ruler, a pulse of

ultrasonic sound is generated and travels to the bottom of the lake and reflected by it. The time taken

by the pulse to travel to the bottom of the lake and return to the ruler is 0.35 s. If the speed of sound

in the freshwater is 1482 ms-1

, calculate the depth of the lake.

Information : v = 1482 ms-1

, t = 0.35 s

d = v x

= 1482 x (0.35/2)

= 259.35 m

1.6


1-23

1. A thin guitar string is strummed hard. It will

produce a loud and high pitch sound.

The most suitable graph to represent the

above situation is

4

2. Diagram 1.63 shows a submarine

transmitting ultrasonic waves directed at a

big rock on the sea bed. After 10 seconds, the

subimarine detects the reflected wave.

Diagram 1.63

Calculate the distance of the submarine from

the big rock.

[ velocity of ultrasonic wave = 1 560 ms-1

]

A. 3.9 km D. 31.2 km

B. 7.8 km E. 156.6 km

C. 15.6 km

3. A radar transmits a signal towards an

aeroplane. The velocity if the signal is

3.0 x 108 ms

-1. After 4.0 x 10

-3 s, the radar

detects the reflected signal. What is the

distance of the aeroplane from the radar?

A. 2.4 x 10 6 m C. 6.0 x 10

5 m

B. 1.2 x 10 6 m D. 1.5 x 10

5 m

3. Diagram 1.64 shows a stretched steel wire

which produces a loud sound when the wire

is plucked.

Diagram 1.64

A loud sound means

A. a high speed C. a high frequency

B. a large amplitude D. a large wavelength

4. Which of the following corresponds to the

highest pitch of sound?

5. Two notes are played on a guitar. The second

is louder and has a higher pitch. The second

note is

A higher in amplitude and lower in frequency

B higher in both amplitude in frequency

C lower in amplitude and higher in frequency

D lower in both amplitude and frequency


1-24

6. Diagram 1.65 shows an ultrasonic waves

transmitted from a boat to the seabed to

determine the depth, D, of the sea. The speed

of the ultrasonic waves in water is 1 500 ms-1

.

The echo of the waves is received 2.0 s after

the transmission.

Diagram 1.65

What is the value of D?

A. 375 m D. 3 000 m

B. 750 m E. 6 000 m

C. 1 500 m

7. Diagram 1.65 shows an audio frequency

generator connected to a speaker and placed

near the corner of a wall. Three students, A,B

and C are standing around the next corner.

The generator and speaker can produce sound

with the same speed but different pitch.

. Diagram 1.65

a) State the physical quantity that affects the

pitch of the sound.

Frequency

(a) When a high pitch sound is generated, only

student C can hear the sound clearly. When

a low pitch sound is generated, all the three

students can hear the sound clearly. Explain

this situation.

High pitch sound has high frequency and

short wavelength.

Frequency inversely proportional to

wavelength.

Sound is not diffracted to student A and

B.

Low pitch sound has low frequency and

longer wavelength.

The sound will diffracted better by the

corner and all student can hear the sound

clearly.

(b) The depth of a sea is 90 m. A ship transmits

an ultrasonic wave of frequency 50 kHz to

the seabed and receives an echo 0.12 s later.

Calculate:

i) The speed of the ultrasonic wave in the

water.

d = v x

90 = v x (0.12/2)

V = 1500 ms-1

(ii) The wavelength of the ultrasonic wave in

the water.

v = fλ

λ = v / f

= 1.5x 103

5 x 104

= 3 x 10-2

m

8. Diagram 1.66 shows an airport radar

transmitting microwave signals. Microwave

are transmitted to determine the position of

aeroplane.

Diagram 1.66

a) Microwave are a type of electromagnetic

wave.


1-25

b) The radar transmits a signal at a velocity of

3.0 x 108 ms

-1 towards the aeroplane P and

detects the reflected signal 4.0 x 10-4

s later.

Calculate the distance of P from the radar

transmitter at that time.

d = vt

2

d = 3.0 x 108 (4.0 x 10

-4)

2

= 60 000 m

c) The radar detects the same signal after

reflection by another aeroplane Q. The

signal from Q arrives later than the signal

from P.

(i) Compare the distance of P and Q from

the radar.

The distance of Q is further from radar

compare to P.

(ii) State how the difference of the distance of

P and Q from the radar is determine any

time.

Determine the shortest distance from P to

radar and from Q to radar.

9. The diagram below shows a fishing boat is

detecting a shoal of fish by using a sonar

system which has a high frequency sound

wave.

.

(a) State the sound wave phenomenon

for detecting the shoal of fish.

Reflection .

(b) Explain why sonar used a high frequency

sound wave.

Ultrasonic waves can transfer more energy

(c) If the time to detect the shoal of fish is 1/15

seconds, calculate the distance of the fishes

from the boat if the speed of the sound waves

in water is 1500 ms-1

.

d = vt

2

= 1 500 x (1/15)

2

= 50 m

(d) Explain why does the speed of sound

in water is greater than the speed of

sound in air? [2 m]

because water is denser than air. The

molecules are closer in water and it will

travel faster.

(e) Name one application of sonar.

ultra sound.


1-26

ANALYSING ELECTROMAGNETIC WAVES.

Describe the

electromagnetic

spectrum.

Electromagnetic spectrum consists of a group of waves with similar and arranged in

increasing frequencies and decreasing wavelengths.

list sources of

electromagnetic

waves

Radio waves : radio and television transmitter

Microwaves : radar transmitter and microwaves oven.

Infrared rays : sun

Visible light : sun, LED, electric bulbs..

Ultraviolet rays : sun, sparks, mercury lamps.....

X-rays : x-ray tubes

Gamma rays : radioactive substance, cosmic rays.

describe the

properties of

electromagnetic

waves

Fill in the box / blank with the correct answer.

Long waves short waves micro waves infra red Ultra violet X – rays gamma rays

t

1.

1. Electromagnetic spectrum consist of a group of waves with similar natures.

3. It is arranged in increasing frequencies and decreasing wavelengths .

4. Radio wave have the longest ( longest / shortest ) wavelength and low ( low / high)

frequency waves.

5. Gamma rays have the shortest ( longest / shortest) wavelength and high ( low / high)

frequency waves.

6. Electromagnetic waves consist of combination of oscillating ( interaction / oscillating)

electric and magnetic ( force / magnetic) field perpendicular

7. Electromagnetic wave is a transverse ( transverse / longitudinal ) wave.

1.7

Long waves gamma

rays X –

rays short waves Ultra violet

infrared micro waves


1-27

8. INFRARED RAY MICROWAVES RADIO WAVES VISIBLE LIGHT

ULTRAVIOLET RAYS X-RAY S GAMMA RAY

Longest wavelength ( 106 – 10

-1 m)

Used for broadcasting and communication RADIO WAVES

Carries along wit it audio, video and other

encoded information.

Have shorter wavelength . ( 10-1

– 10-3

m)

Suitable for satellite- based communication systems,

mobile phone networks

Military uses it for spying and surveillance. MICROWAVES

The range of wavelength is between 10-3

– 10-6

m.

Ordinary ovens,grills and toaster use this wave to

cook food.

Can transmit information through the air to operate

televisions and video recorders by remote control.

Also used in night vision devices. INFRARED RAY

Easily detected by human and animal eyes.

Used in photography and can be transmitted through VISIBLE LIGHT

optical fibre


– 10-9

m.

Can cause skin to tan and may result in skin cancer.

Can kill living cells,bacteria and germs. ULTRAVIOLET RAYS


– 10-12

m.

Widely used in the medical field.

Used to inspect metal castings and welded joints for hidden X-RAY S

faults.

Shortest wavelength in the electromagnetic spectrum.

Used in radiotheraphy to treat cancer

Used sterillisation process GAMMA RAY

Physics Module Form 5 GCKL 2010

28

1. Which of the following statements is true

about electromagnetic waves?

A. They are longitudinal waves.

B. They are waves that require a medium to

travel.

C. The velocity of the waves is influenced by

the wavelength

D. They consist of both magnetic field and

electric field.

2. What is the correct relationship between the

wave length of an electromagnetic radiation

and the energy it carries.

Wave length Energy carried

A. Short High

B. Short Low

C. Long High

D. Long Low

3. Diagram 1.7 shows an electromagnet

spectrum.

Diagram 1.7

The waves at P,Q,R and S are

A B C D

P Ultraviolet X – ray Microwave X ray

Q X –ray Ultraviolet Infrared Microwave

R Microwave Infrared Ultraviolet x-ray

S infrared Microwave X ray microwave

4. At an airport, a passenger’s bag is placed in

the baggage scanner.

The content in the bag are examined by using

A. X-ray C. Ultraviolet ray

B. Gamma rays D. Infrared rays

5. Which is the correct arrangement of

electromagnetic waves in order of increasing

frequency?

A. Infrared rays, Microwaves, Gamma rays,

Ultraviolet rays.

B. Gamma rays,, Ultraviolet rays, Infrared

rays, Microwaves.

C. Microwaves, Infrared rays, Ultraviolet

rays, Gamma rays.

D. Ultraviolet rays, Gamma rays,

Microwaves, Infrared rays.

6. Figure 1.8 (a) shows the x-rays film of a

patient. Figure 1.8 (b) shows the microwave

from the satellite used in communication.

Figure 1.8 (a) Figure 1.8

a) Observe the figures and state two similarities

between the waves.

Both are transverse waves/They transfer

energy from one place to another/

They can travel through vacuum with the

speed of light.

Physics Module Form 5 GCKL 2010

29

b) Which group does these two waves belong to?

Electromagnetic waves

c) Name one other wave that has the same

properties.

Radio waves / gamma rays / ultra violet /

visible light / infra red

d) Microwaves travel at a speed of 3.0 x 108ms

-1 in a

vacuum and have a frequency of 15 x 1010

Hz.

i) Calculate the wavelength of these

microwaves.

λ = v/f

=3.0 x 108 ms

-1

15 x 1010

Hz.

= 2.0 x 10-3

m.

Physics Module Form 5 GCKL 2010 - KS Thong's Blog | PHYSICS · PDF file · 2012-02-012012-02-01 · Physics Module Form 5 chapter 1 : Waves GCKL 2011 1-2 5. In the...

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