(a)

State what is meant by the diffraction of a wave.
(b) A laser produces a narrow beam of coherent light of wavelength 632 nm . The beam is incident normally on a diffraction grating, as shown in Fig. 4.1.

[ 2 ]

[Maximum number: 1]

A loudspeaker is playing music in a room. The door to the room is open and has a width of 0.80 m .

Sound waves of many different frequencies pass through the doorway and diffract. The speed of sound in air is $340 \mathrm{~ms}^{-1}$ .

Which frequency of sound wave diffracts the most as it passes through the doorway?

$2.4 \times 10^{-3} \mathrm{~Hz}$

$8.0 \times 10^{-1} \mathrm{~Hz}$

$2.7 \times 10^{2} \mathrm{~Hz}$

$4.3 \times 10^{2} \mathrm{~Hz}$

(a)

The width of each slit in (b) is decreased by the same amount. There is no change to the separation of the slits.

Describe and explain the effect, if any, of this change on the appearance of the interference pattern.

[ 2 ]

[Maximum number: 1]

Diagram 1 shows a ripple tank experiment in which plane waves are diffracted through a narrow slit in a metal sheet.

Diagram 2 shows the same tank with a slit of greater width.
In each case, the pattern of the waves incident on the slit and the emergent pattern are shown.

Which action would cause the waves in diagram 1 to be diffracted less and so produce an emergent pattern closer to that shown in diagram 2?

increasing the frequency of vibration of the bar

increasing the speed of the waves by making the water in the tank deeper

reducing the amplitude of vibration of the bar

reducing the length of the vibrating bar

[Maximum number: 1]

Diagram 1 shows a ripple tank experiment in which plane waves are diffracted through a narrow slit in a metal sheet.
Diagram 2 shows the same tank with a slit of greater width.
In each case, the pattern of the waves incident on the slit and the emergent pattern are shown.

Which action would cause the waves in diagram 1 to be diffracted less and so produce an emergent pattern closer to that shown in diagram 2?

increasing the frequency of vibration of the bar

increasing the speed of the waves by making the water in the tank deeper

reducing the amplitude of vibration of the bar

reducing the length of the vibrating bar

[Maximum number: 1]

Which statement gives a condition that enables diffraction to occur?

A source of waves moves towards a stationary observer.

A wave is partially blocked by an obstacle.

Two coherent waves are superposed.

Two waves are travelling through the same part of a medium in opposite directions.

[Maximum number: 1]

Water waves of wavelength $\lambda$ are formed in a ripple tank. The waves are diffracted as they pass through a narrow gap of width d ( d is greater than $\lambda$ ).

Which gap width and which wavelength will cause the largest decrease in the amount of diffraction?

gap width

wavelength

$\frac{1}{2} d$

$\frac{1}{2} \lambda$

$\frac{1}{2} d$

$2 \lambda$

2 d

$\frac{1}{2} \lambda$

2 d

$2 \lambda$

[Maximum number: 1]

A transmitting mast sends out microwaves of wavelength 1.5 cm and radio waves of wavelength 1.5 km .

A receiving aerial behind a mountain can detect the radio waves but not the microwaves.
What is the reason for this?

The radio waves are coherent but the microwaves are not.

The radio waves are diffracted around the mountain but the microwaves are not.

The radio waves are reflected by the mountain but the microwaves are not.

The radio waves travel at the speed of light but the microwaves do not.

[Maximum number: 1]

A sound wave of wavelength 0.50 m passes through a doorway of width 1.0 m between two rooms.

Which change increases the amount of diffraction that takes place?

Double the amplitude of the sound wave.

Double the width of the doorway.

Halve the frequency of the sound wave.

Halve the period of the sound wave.

[Maximum number: 1]

Water waves in a ripple tank are made to pass through a small gap, as shown.
Which diagram shows the waves after they have passed through the gap?