Physics (AS & A Level) · May / June 2018 · Paper 12 · Question 26

The diagram shows apparatus for the measurement of the frequency of a sound wave. Sound of the unknown frequency is reflected back from a metal plate. A microphone placed at a distance D from the metal plate detects the sound intensity. A minimum intensity is detected with D = 12.0 cm. The plate is moved further away from the microphone until the next minimum is detected with D = 15.0 cm. The speed of sound in air is 336 m s–1. What is the frequency of the sound?

1. A56 Hz
2. B112 Hz
3. C5600 Hz
4. D11 200 Hz

As printed in the paper