Physics (AS & A Level) · Oct / Nov 2020 · Paper 11 · Question 28

Two loudspeakers are placed near to each other and facing in the same direction. A microphone connected to an oscilloscope is moved along a line some distance away from the loudspeakers, as shown. [diagram: loudspeakers, microphone, path of microphone] Which statement about the waves emitted by the loudspeakers is not a necessary condition for the microphone to detect a fixed point along the line where there is no sound?

1. AThe waves must be emitted in phase.
2. BThe waves must be emitted with a similar amplitude.
3. CThe waves must have the same frequency.
4. DThe waves must have the same wavelength.

As printed in the paper