For a progressive transverse wave, what describes the term diffraction?
Correct Answer: \( \boxed{\mathrm{B}} \)
Diffraction is the spreading of waves when they pass through a gap or around the edge of an obstacle.
The other options describe the Doppler effect, polarisation and the principle of superposition.
Therefore, the correct answer is (B).
A light wave passes through a single slit and a diffraction pattern forms.
What happens to the frequency and the speed of the wave when it is diffracted?
| frequency | speed | |
|---|---|---|
| (A) | decreases | increases |
| (B) | increases | decreases |
| (C) | no change | decreases |
| (D) | no change | no change |
Correct Answer: \( \boxed{\mathrm{D}} \)
Diffraction changes only the direction of propagation of the wave.
Since the light remains in the same medium, both its frequency and speed remain unchanged.
Therefore, the correct answer is (D).
The diagram shows a water wave in a shallow tank. The wave is diffracted through a gap in a barrier and spreads. The wavelength of the wave is much smaller than the width of the gap.
The wavelength of the wave and the width of the gap are both changed by a small amount.
Which combination of changes must increase the amount of spreading due to diffraction?
| Wavelength | Width of gap | |
| (A) | decreases | decreases |
| (B) | decreases | increases |
| (C) | increases | decreases |
| (D) | increases | increases |
Correct Answer: \( \boxed{\mathrm{C}} \)
The amount of diffraction depends on the ratio of wavelength to gap width.
Diffraction increases when the wavelength becomes larger and/or the gap becomes smaller.
Only option (C) increases the wavelength while decreasing the gap width, guaranteeing greater spreading.
Therefore, the correct answer is (C).
