1.4 diffraction - pembelauan gelombang fizik spm

$: 1.4 diffraction - Pembelauan Gelombang Fizik SPM$
Chapter1: Waves1.4 Analysing Diffraction of Waves

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.


• 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.


• 3 Characteristics of diffracted waves:

• (a) Frequency, wavelength and speed of waves do not change.


• 3 Characteristics of diffracted waves:

• (b) Changes in the direction of propagation and the pattern of the 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?



• Hypothesis

• If the size of the aperture is small enough, the diffractive effects on the water wave become obvious (visible).


• (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



• Apparatus/Materials

• Ripple tank, metal bars, mechanical stroboscope and piece of white paper.



• Procedure

• 1 A ripple tank is filled with water and set up as shown in Figure 1.41.



• 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.


• (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.


• (I) Fixed wavelength• Procedure• 4 The pattern of the waves

before and after passing the slit is observed and drawn.



• Procedure

• 5 Steps 2 to 4 are repeated with different widths for

slits: 6 cm and 2 cm respectively.


• (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.


• (I) Fixed wavelength• Procedure• 7 Steps 3 and 4 are repeated with different

lengths of metal bar: 6 cm and 2 cm respectively.



• 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.


• Conclusion

• As the size of the aperture or obstacle decreases, the effect of diffraction becomes obvious. The hypothesis is accepted.


• (II) Fixed size of aperture

• What is the relationship between the frequency of a water wave and the effects of diffraction?



• Hypothesis

• The effects of diffraction of the water wave become more obvious as the frequency of the wave decreases.


• (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



• Procedure

• 1 A ripple tank is filled with water and set up as shown in Figure 1.41.


• (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.



• Procedure

• 3 The vibrator is switched on. The frequency of the

water wave is gradually increased by adjusting the

rheostat.



• Procedure

• 4 The patterns of the waves passing through the slit at different frequencies are observed and drawn.



• 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.



• Conclusion

• The effect of diffraction of a water wave became obvious as the frequency of the wave decreases.

• The hypothesis is accepted


• 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?


• 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

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 obviousas the size of the slit increases. This is because the wavelengths of light are very short.


• 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).


• 3. Observation:•• (a) Narrow slit

• (b) Wider slit

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?


• Hypothesis

• The person can hear the sound of the radio although it is behind an obstacle.


• 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.


• 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.


• Results

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


• Discussion

• The sound of the radio spreads around the come the wall due to diffraction of sound.


• Conclusion

• The sound is able to spread around a space or an obstacle. The hypothesis is valid.

1.4 diffraction - pembelauan gelombang fizik spm

Education

effect of diffraction

effects of diffraction

waves chapter1

plane waves

speed of waves

obstacle decreases

wavelength of water

pieces of metal bars