Physics (AS & A Level) · Oct / Nov 2022 · Paper 12 · Question 26

The wavelength of sound in air may be determined by using stationary waves. In one experiment, a loudspeaker produces a sound wave of constant frequency which is reflected directly back along its original path by a metal plate approximately 1 m away. A microphone connected to a cathode-ray oscilloscope (CRO) is moved between the loudspeaker and plate to identify regions of high sound intensity ('loud' spots) and low sound intensity ('quiet' spots). The wavelength of the sound is determined using the least possible number of measured quantities. Which row shows the quantities that are needed?

1. Afrequency of sound ✓, mean separation of 'quiet' spots ✓, speed of sound in air ✗
2. Bfrequency of sound ✓, mean separation of 'quiet' spots ✗, speed of sound in air ✓
3. Cfrequency of sound ✓, mean separation of 'quiet' spots ✗, speed of sound in air ✗
4. Dfrequency of sound ✗, mean separation of 'quiet' spots ✓, speed of sound in air ✗

As printed in the paper