5.5 Diffraction of waves

MODUL PDP SPM PASCA PKP
NEGERI PERAK 2020

PHYSICS Form 4

5.5: Diffraction of Waves

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5.5 Diffraction of Waves

Learning Standard:

Pupils are able to:

• describe diffraction of waves from the following aspects:
(i) wavelength, λ
(ii) frequency, f
(iii) speed, v
(iv) amplitude, A
(v) direction of propagation of waves

• determine factors affecting diffraction of waves.
• draw diagrams to show the pattern of diffraction of water waves and the effect of

diffraction of light waves.
• explain the applications of diffraction of waves in daily life.

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5.5 Diffraction of Waves

1. Photograph 1 shows the embankment built in Marang, Terengganu.
plane wavefront

embankment circular
wavefront

Photograph 1. Embankment in Marang, Terengganu

2. Photograph 1 shows the sea waves spread out while propagating through the gap in
the embankment.

3. The phenomenon occurs in photograph 1 is diffraction of waves.

4. Diffraction of waves can happen to:
(i) water waves
(ii) light waves
(iii) sound waves

5. Definition of diffraction of waves: Spreading of waves when the waves propagates
through a slit/ side of a barrier.

6. The effects of diffraction on the characteristics of the waves:
(i) Table shows the effects of the diffraction on characteristics of waves.

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(ii) The figures below shows the pattern of diffraction of water, light and sound
waves.

Figure 2. Diffraction pattern of water wave Figure 3. Diffraction pattern of sound wave
Figure 4. Diffraction patterns of light waves

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7. Table 1 shows the patterns of diffracted water waves in a simulated ripple tank and
sketches of the wavefront.

Table 1. Effects of size of slits and wavelength on pattern of diffracted waves
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8. Diffraction of waves is influenced by the size of slit and wavelength as shown in Figure
5.

Figure 5. Factors which influence the diffraction of waves and their effects
9. Figure 6 shows the examples of diffraction of water, light and sound waves.

Figure 6. Diffraction of water, light and sound waves
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5.5 MIND MAP

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5.5 FAQ

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

A Diffraction is the bending of waves around obstacles and openings. The
amount of diffraction increases with increasing wavelength.

2 Q Does frequency change in diffraction?
A Diffraction is the bending of a wave in the same medium. As such , there is
no change in medium , hence the wavelength, frequency, speed , time period
will all remain same.

3 Q How does diffraction affect wavelength?
A The amount of diffraction increases with increasing wavelength and
decreases with decreasing wavelength. In fact, when the wavelength of the
waves is smaller than the obstacle, no noticeable diffraction occurs.

4 Q Why does sound diffract more than light?
A Sound wave diffracted more than light wave because the wavelength of
sound waves are longer than light waves.

5 Q Why monochromatic light is used in diffraction?
A Monochromatic light is light of a single wavelength, or at least very narrow
bandwidth.

6 Q How is diffraction used in everyday life?
A One of the most evident examples of diffraction are those involving light; for
example, when you take a keen look at a CD or DVD the closely spaced tracks
on a CD or DVD act as a diffraction grating to form the familiar rainbow
pattern.

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5.5 Exercise

SECTION A
1 The diagram shows an arrangement of apparatus for light diffraction experiment.

Which diffraction pattern appears on the screen?

[MENGETAHUI]

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2 Diagram 2 shows water waves passing through an opening, x, of a barrier.

Diagram 2

Which statement is correct?

[MEMAHAMI]

A The water waves are refracted.

B The amplitude of the waves will increase after passing through the opening.

C The spreading of water waves will increase when the opening at x is reduced

D Changing the wavelength of the waves will not affect the spreading.

3 Diagram 3 shows water waves passing a concrete obstruction in a river.
.

Which phenomenon explains the change in wave pattern at X ? [MENGETAHUI]

A Reflection
B Refraction
C Diffraction
D Interference

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4 The siren of a fire truck has low frequency so that the sound wave can
[MEMAHAMI]

A be reflected easily.
B be refracted easily.
C undergo total internal reflection easily.
D be diffracted easily.
5 Which of the following diagrams shows the diffraction of water waves?

[MENGETAHUI]
AC

BD

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SECTION B

6 Diagram 6.1 shows the arrangement of the apparatus for an experiment to study a wave
phenomenon.

Diagram 6.1
Diagram 6.2 shows the bright and dark bands of the wave pattern formed on the screen
when plane waves pass through narrow and wipe gaps.

Diagram 6.2

a) What is the meaning of wavelength?

[MENGETAHUI]

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

b) Based on the Diagram 6.2.
[MENGANALISIS]

i) Compare the wave patterns of the waves before and after they pass through
the gaps

……………………………………………………………………………………

……………………………………………………………………………………
[2 mark]

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ii) Compare the wavelengths of the waves before and after they pass through the
gaps

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

(iii) state the relationship between the size of the gaps and the wave patterns.

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

(iv) Name the physics phenomenon involved
[MENGETAHUI]

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

7 Diagram 7.1 shows a water waves passing through a log that floats in water.
Diagram 7.2 shows a student standing at one corner of a building at B who can hear
the sound from a loudspeaker at A.

Diagram 7.1 Diagram 7.2

a) Based on the Diagram 7.1 and 7.2.

(i) what happens to the wave after passing round the log and the corner of the
building?
[MEMAHAMI]

……………………………………………………………………………………
………………………………………

[1 mark]

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(ii) What happens to the amplitude of the waves after passing round the
log and the corner of the building? Explain your answer.
[MEMAHAMI]

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

(iii) name the wave phenomenon that is related to Diagram 7.1 and Diagram
7.2.
[MENGETAHUI]

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

(iv) what will happen to the speed of the water waves after passing through the
log?
[MEMAHAMI]

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

(b) Referring to Diagram 7.1, what will happen to a floating object that is placed at
[MEMAHAMI]

(i) P?
……………………………………………………………………………………

[1 mark]
(ii) Q
……………………………………………………………………………………

[1 mark]
(c) Name one other wave phenomenon that occurs in Diagram 7.1.

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

[1 mark]

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5.5 QR CODE

5.5 Diffraction of waves QR CODE

Title link

Diffraction | Waves | https://youtu.be/7hNbcHmCey0
Physics

Diffraction of waves https://youtu.be/_JQnvwA-9Ho

Apertures and https://youtu.be/BH0NfVUTWG4
Diffraction

REINFORCEMENT https://drive.google.com/file/d/1t3h6YElNfTL26tsfe
TEST HJPlupXkxaF5a7y/view?usp=sharing

ANSWER https://drive.google.com/file/d/1bL670F7wMZVw62
REINFORCEMENT cC8REf8Fy3TgFmt-3x/view?usp=sharing
TEST

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5.5 Answer

SECTION A

1. D
2. C
3. C
4. D
5. D

SECTION B
1.

6 a) Distance between two successive points that are in phase

b)
i)Before passing through the narrow and wide gaps, plane wavefronts can be
observed.

After passing through the narrow gaps, the waves emerging from the gap have
circular wavefronts

ii) The wavelengths of the waves before and after passing through the narrow and
wide gaps are the same

(iii) The narrower the size of the gap is, the bigger the bending/ curvature of the
wave will be.

(iv) Diffraction of waves

7 a(i) Wave diffracts / spreads to a bigger area
(ii) Amplitude of the waves decreases
Energy decreases
(iii) Diffraction
(iv) Unchanged/same
b(i) Vibrates/Oscillates
(ii) Stationary
(c) Reflection

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