Physics (AS & A Level) · Feb / March 2021 · Paper 12 · Question 23

A loudspeaker emitting a sound wave of a single frequency is placed a distance L from a reflecting surface, as shown. A stationary wave is formed with an antinode at the loudspeaker. A microphone is moved from the loudspeaker to the reflector. Before the microphone reaches the reflector, it detects four points where the sound intensity is a minimum. What is the wavelength of the sound wave?

1. A\frac{2L}{9}
2. B\frac{2L}{8}
3. C\frac{4L}{9}
4. D\frac{4L}{8}

As printed in the paper