The document discusses the diffraction of waves, including water waves, light waves, and sound waves. It provides details on experiments investigating how diffraction is affected by the size of an aperture or obstacle and the wavelength of the waves. The key points are: 1) Diffraction occurs when waves pass through a small aperture or around a small obstacle, causing the waves to spread out. 2) The effect of diffraction is more obvious when the aperture/obstacle size is small and the wavelength is large. 3) Experiments with water waves showed greater diffraction effects for smaller apertures/obstacles and lower wave frequencies.

1. Chapter1: Waves
1.4 Analysing Diffraction of
Waves

2. 1.4 Analysing Diffraction of Waves
• 1 Diffraction of waves is a phenomenon in which
waves spread out as they pass through an aperture or
round a small obstacle.

3. 1.4 Analysing Diffraction of Waves
• 2 The effect of diffraction is obvious only if
• (a) the size of the aperture or obstacle is small
enough,
• (b) the wavelength is large enough.

4. 1.4 Analysing Diffraction of Waves
• 3 Characteristics of diffracted waves:
• (a) Frequency, wavelength and speed of waves
do not change.

5. 1.4 Analysing Diffraction of Waves
• 3 Characteristics of diffracted
waves:
• (b) Changes in the direction
of propagation and the
pattern of the waves.

6. 1.4 Analysing Diffraction of Waves
• Experiment 1.6: to investigate the pattern of
diffracted water waves
• (I) Fixed wavelength
• Problem statement
• What is the relationship between the size of the
aperture or obstacle and the effects of
diffraction of water waves?

7. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Hypothesis
• If the size of the aperture is small enough, the diffractive
effects on the water wave become obvious (visible).

8. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Variables
• (a) Manipulated : Size of aperture or obstacle
• (b) Responding : Pattern of diffracted water waves
• (c) Fixed : Wavelength of water wave, frequency of
dipper and its distance from the aperture or obstacle

9. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Apparatus/Materials
• Ripple tank, metal bars,
mechanical stroboscope and
piece of white paper.

10. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 1 A ripple tank is filled
with water and set up as
shown in Figure 1.41.

11. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 2 Two pieces of metal bars
are positioned to form a slit
of width 10 cm at a distance
of 5 cm from the vibrating
wooden bar.

12. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 3 The dipper is switched on
and the rheostat is adjusted so
that the wooden bar produces
plane waves with a
wavelength of approximately
4 cm.

13. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 4 The pattern of the waves
before and after passing the slit
is observed and drawn.

14. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 5 Steps 2 to 4 are repeated with different widths for
slits: 6 cm and 2 cm respectively.

15. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 6 The two pieces of metal bars are replaced with a
single metal bar of length 10 cm placed centrally
at a distance of 5 cm from the vibrating wooden bar.

16. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Procedure
• 7 Steps 3 and 4 are repeated with different
lengths of metal bar: 6 cm and 2 cm
respectively.

17. 1.4 Analysing Diffraction of Waves
• (I) Fixed wavelength
• Result
(I) Fixed wavelength
(a) Small slit (b) Large slit (c) Large obstacle (d) Small obstacle
  a, the effect
of diffraction is
very obvious.
 < a, the effect
of diffraction is
not obvious.
The effect of
diffraction is not
obvious.
The effect of
diffraction is
obvious.

18. 1.4 Analysing Diffraction of Waves
• Conclusion
• As the size of the aperture or obstacle decreases,
the effect of diffraction becomes obvious. The
hypothesis is accepted.

19. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• What is the relationship between the frequency
of a water wave and the effects of diffraction?

20. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Hypothesis
• The effects of diffraction of the water wave
become more obvious as the frequency of the
wave decreases.

21. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Variables
• (a) Manipulated : Frequency of dipper (i.e. frequency of
water wave)
• (b) Responding : Pattern of diffracted waves
• (c) Fixed : Size of slit and its distance from the dipper

22. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Procedure
• 1 A ripple tank is filled with water and set up
as shown in Figure 1.41.

23. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Procedure
• 2 Two pieces of metal bars are positioned to
form a slit of 5 cm wide 5 cm away from the
vibrating wooden bar.

24. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Procedure
• 3 The vibrator is switched on. The frequency of the
water wave is gradually increased by adjusting the
rheostat.

25. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Procedure
• 4 The patterns of the waves passing through
the slit at different frequencies are observed and
drawn.

26. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Results/Discussion
(II) Fixed size of slit
(a) Short 
 < a, the effect of
diffraction is not obvious.
(b) Long 
  a, the effect of
diffraction is very obvious.

27. 1.4 Analysing Diffraction of Waves
• (II) Fixed size of aperture
• Conclusion
• The effect of diffraction of a water wave became obvious
as the frequency of the wave decreases.
• The hypothesis is accepted

28. 1.4 Analysing Diffraction of Waves
• Example 9
• In an experiment on the diffraction of water waves, a
dipper with a frequency of 8 Hz produces waves with a
wavelength of 2 cm. If the frequency of the dipper is 10
Hz what is the wavelength of the water waves produced?

29. 1.4 Analysing Diffraction of Waves
• Example 9
• Solution
• Using the formula:
• where is constant (as the velocity of the wave is constant
in a ripple tank of uniform depth).
•
fv 

30. Diffraction of Light
• 1 Light is diffracted if it
passes through a narrow
slit comparable in size to
its wavelength. However,
the effect is not obvious
as the size of the slit
increases. This is because
the wavelengths of light
are very short.

31. Diffraction of Light
• 2. Diffraction of light is hardly noticeable
compared with diffraction of sound waves and
water waves because the wavelength of light is
very short (approximately 10-7 m).

32. Diffraction of Light
• 3. Observation:
•
• (a) Narrow slit
• (b) Wider slit

33. Diffraction of Sound Waves
• Experiment 1.7: To investigate the diffraction of
sound waves
• Problem statement
• Can a person hear the sound of a radio which is
hidden behind an obstacle?

34. Diffraction of Sound Waves
• Hypothesis
• The person can hear the sound of the radio
although it is behind an obstacle.

35. Diffraction of Sound Waves
• Procedure
• 1 A radio is placed nearby a corner of a wall.
• 2 A student is requested to stand on the other side of
the corner of the wall so that the radio is beyond his
vision.

36. Diffraction of Sound Waves
• Procedure
• 3 The radio is turned on and the student is requested
to listen to the radio.
• 4 The position of the radio is changed and the effect
on the sound of the radio is listened to.

37. Diffraction of Sound Waves
• Results
• The student is able to hear the sound of the radio
although it is behind the wall (beyond his vision).

38. Diffraction of Sound Waves
• Discussion
• The sound of the radio spreads around the come the wall
due to diffraction of sound.

39. Diffraction of Sound Waves
• Conclusion
• The sound is able to spread
around a space or an
obstacle. The hypothesis is
valid.