5.4 Refraction of waves

MODUL PDP SPM PASCA PKP
NEGERI PERAK 2020

PHYSICS Form 4

5.4: Refraction of Waves

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5.4 Refraction of Waves

Learning Standard:

Pupils are able to:

• describe refraction of waves from the following aspects:
(i) angle of incidence, i
(ii) angle of refraction, r
(iii) wavelength, λ
(iv) frequency, f
(v) speed, v
(vi) direction of propagation of waves

• draw diagrams ot show the refraction of waves for two different depths.
• explain natural phenomena of refraction of waves in daily life.
• solve problems involving refraction of waves.

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5.4 Refraction of Waves

1. Photograph 1 shows the curving waterfront of the sea when approaching the
shoreline.

Photograph 1. Refraction of sea waves
2. The phenomenon of curving wavefront is caused by refraction of waves.
3. Definition of refraction of waves: The change in direction of propagation of waves

caused by the change in the velocity of waves when the waves propagate from one
medium to another.
4. Additional information:
(i) Speed of water wave is influenced by depth of water.
(ii) Speed of sound wave is influenced by density of air.
(iii) Speed of light wave is influenced by optical density of medium
5. Effects of refraction on the characteristics of waves:
(i) Figure 1 shows propagation of water waves from deep water region to shallow

water region.

Wave speed, V1
= high

Wave speed, V2
= low

Figure 1. Propagation of water waves from deep water region to shallow water region.

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(ii) Figure 2 shows propagation of water waves from shallow water region to deep
water region.

Wave speed, V1
= low

Wave speed, V2
= high

Figure 2. Propagation of water waves from shallow water region to deep water
region.

(iii) Table 1 shows effects of refraction on the characteristics of waves

Table 1. Effects of refraction on the characteristics of waves

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6. The method of drawing diagram of refraction of plane water waves:

Arrowed line AB 1A Normal line perpendicular to the
perpendicular to the 2 boundary of the deep region and
incident wavefront,
shallow region at B.

representing direction of Normal

propagation of the

incident wave. Perpendicular/ 90° Perpendicular/ 90°

B

Draw 3 lines perpendicular to

4 BC representing the refracted
wavefronts.

The lines have to be closer to
one another compared to the
incident wavefronts.

C 3 Draw arrowed line BC, nearer to the
normal compared to AB,
representing the direction of
propagation of the refracted wave.

7. Jika gelombang air merambat dari kawasan yang cetek ke kawasan yang dalam, arah
perambatan gelombang biasan haruslah menjauhi garis normal.

8. Phenomena of Refraction of Waves in Daily Life:
(i) During the day, air that is closer to the surface of the earth is hotter, sound
moves faster in hot air than in cold air.
Sound is refracted away from the ground.
Thus, an observer cannot hear sound clearly during the daytime as shown in
Figure 3.

Figure 3. Sound is not heard clearly during the day

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(ii) During the night, air that is closer to the surface of the earth is colder, sound
moves slower in cold air.
Sound is refracted towards the ground.
The observer could hear sound more clearly during the night as shown in
Figure 4.

Figure 4. Sound is heard more clearly during the night

(iii) Phenomenon of refraction of sea water is as shown in Figure 5.

Speed of the water waves Deep region Wavefront
decreases, wavelengths Shallow region curves & follows
the shape of the
becomes shorter.
shoreline.

Wavefront of the Speed of the
water is almost water waves
straight and parallel
because water waves increases,
move at a uniform wavelength
becomes longer.
speed.

Figure 5. Refraction of sea waves

 Refraction of water waves causes water wave energy to converge
towards the cape, the amplitude of waves at cape is bigger.

 At the bay, water wave energy diverges and spread out to a wider
region, the amplitude of waves at bay is smaller & water is calmer.

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9. Solving Problems Involving Refraction of Waves:
(i) Figure 6 shows changes in speed and wavelength when water waves propagate
from deep region to shallow region.

Figure 6. Propagation of water waves from deep region to shallow region
(ii) Refraction of waves is caused by the change in speed of waves:

 Speed of waves, 1& 2 change when depth of water changes,
 Wavelength, ƛ1& ƛ2 also change,
 Frequency of waves, does not change because wave frequency is

determined by the frequency of vibrations at the source of the wave.

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10. Example 1:
A plane wave which has a wavelength of 2 and speed of 8 −1 propagates across
a shallow region. When the wave enters the deep region, wave speed becomes 12 −1.
Determine the value of the wavelength in the deep region.

Shallow region: Deep region:
, 1 = ℎ8, 1 = 2−1 , 2 = 1 2 ℎ, 2 = −?1

1 = 2
1
2 12
8 = 2
2
8 2 = 12

2 = 12 × 8 = 3
2
11. Example 2:

Figure 7 shows propagation of water wave from region P to region Q of different
depths. Speed of the wave is 18 −1 in region P. Determine the speed of wave in

region Q.

1 2

Figure 7

4 1 = 12 8 2 = 12
1 =
12 2 = 12
4 8
1 = 3 2 = 1.5
, 1 = 18 −1 , 2 = ? −1

1 = 2
1 22
18
3= 1.5

2 = 18 = 9 −1
3 × 1.5

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5.4 MIND MAP

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5.4 FAQ

No Questions and Answers
1 Q What is the refraction of a wave?

A Refraction of waves involves a change in the direction of waves as they pass
from one medium to another. Refraction, or the bending of the path of the

waves, is accompanied by a change in speed and wavelength of the waves.

2 Q What is the main cause of refraction?

A Refraction is the phenomenon of bending of light at the boundary of two
mediums. Refraction is caused due to the change in speed of light when it

enters from one medium to another.

3 Q Why is there no refraction at zero degrees?

A So, the angle of incidence is zero and hence the angle of refraction is also
zero. In other words, the ray which is incident normally on the interface
between the two different media, propagates un deviated from one medium
to other and there is no refraction.

4 Q Does wavelength change during refraction?

A Refraction is an effect that occurs when a light wave, incident at an angle
away from the normal, passes a boundary from one medium into another in
which there is a change in velocity of the light. The wavelength decreases as
the light enters the medium and the light wave changes direction.

5 Q Why is sound heard better at night than day time?

A Actually, sound transmits farther at night may be related to refraction of
sound waves. First, sound is the vibration of air, and it is a kind of wave
motion. The propagation of sound wave is faster in hot air and slower in cold
air.

6 Q What are three examples of refraction?

A Mirage, bent pencil in glass of water, rainbow, sunset are some examples of
refraction of light.

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5.4 Exercise

SECTION A

1. Which of wave property will not changes when water waves are refracted?
[MENGETAHUI]

A Speed
B Frequency
C Wavelength
D Direction of propagation

2. Diagram shows the propagation of water waves from region X to Y.

XY vX = speed of wave in X

vy = speed of wave in Y
vX

vY

Which is the correct comparison of the wave speed and depth of water in X and Y?

[MENGANALISIS]

Wave speed Depth of water

A vX < vY X <Y

B vX > vY X<Y

C vX < vY X>Y

D vX > vY X>Y

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3. Diagram shows wave fronts that move towards the beach from the sea. It is
observed that the sea is calmer at the bay than at the cape.

The phenomenon is known as [MENGETAHUI]

A Reflection
B Refraction
C Diffraction
D Interference

4. Which of the following sets of velocity, wavelength and frequency of a water wave

that travels from a deep region to a shallow region is correct?

[MENGANALISIS]

Frequency Wavelength Velocity

A No change Decreases Decreases

B No change Increases Increases

C Decreases Decreases Decrease

D No change Increases Decreases

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5. The diagram below shows the velocity of water wave when it travels from deep
region to shallow region.

If the wavelength of the water waves in deep water is 3 cm, what is the
wavelength of the water waves in shallow water?

[MENGAPLIKASI KUANTITATIF]
A 0.16 cm
B 1.8 cm
C 2.0 cm
D 5.0 cm

SECTION B
1. Diagram 1.1 shows the side view of part of two ripple tanks. Water waves of the same

frequency are produced when the motors are switched on.

Diagram 1.1
Diagram 1.2 shows the waves formed on the screen below the ripple tank.

Diagram 1.2
(a) State the meaning of frequency.

[MENGETAHUI]
…………………………………………….…………………………………………

[1 mark]

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(b) Based on diagram 1.1 and diagram 1.2,

[MENGANALISIS]

(i) What happen to the wavelengths in region X and region Y?

…………………………………………….…………………………………………
[1 mark]

(ii) Compare the depths of water in region X and region Y.

…………………………………………….…………………………………………
[1 mark]

(iii) Relate the wavelengths and the depths of water in region X and region Y?.

…………………………………………….…………………………………………
[1 mark]

(iv) State the wave phenomenon which takes place.
[MENGETAHUI]

…………………………………………….…………………………………………
[1 mark]

(c) In Diagram 1.3, the wavefront of sea water follows the shape of shore when it
approaches the shore.

Diagram 1.3
Explain this observation.

[MEMAHAMI]
…………………………………………….…………………………………………
…………………………………………….…………………………………………
…………………………………………….…………………………………………
…………………………………………….…………………………………………

[3 mark]

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5.4 QR CODE

Title 5.4 Refraction of waves QR CODE
link
Water Waves - https://youtu.be/MaGieycP9_U
Shallow to Deep
Water

Waves in a ripple https://youtu.be/iTD5DO5MMgA
tanks

Refraction of https://youtu.be/wO49W5lsP0s
Waves

REINFORCEMENT https://drive.google.com/file/d/1t3h6YElNfTL26tsfeHJPl
TEST upXkxaF5a7y/view?usp=sharing

ANSWER https://drive.google.com/file/d/1bL670F7wMZVw62cC8
REINFORCEMENT REf8Fy3TgFmt-3x/view?usp=sharing
TEST

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5.4 ANSWER

SECTION A

1B
2D
3B
4A
5B

SECTION B Number of complete oscillations made by a particle or number of cycles of
1 (a) wave produced by a source in one second / Number of complete oscillation
in one second
(b)(i) .

the wavelengths in region X and region Y become shorther

(b)(ii) the depths of water in region X is shallower than region Y.

(b)(iii) The deeper the water, the longer the wavelength.

(b)(iv) Wave refraction

(c) - In the middle of the sea, the wavefronts are almost straight because the
depth of water is almost the same.
.
- When the wave approaches the shore, the depth of sea water decreases
and this causes the velocity of wave to decrease.
.
- Refraction occurs and the waves are refracted towards the normal. The
wave fronts follow the shape of shore.

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