Physics 9702 · AS & A Level · Doppler effect for sound waves
Doppler effect for sound waves — practice question
A loudspeaker at rest produces sound with a constant frequency. A microphone is positioned close to the loudspeaker and linked to a cathode-ray oscilloscope (CRO). The trace displayed on the CRO screen is shown in Fig. 5.1. The CRO time-base is adjusted to $5.0 \times 10^{-4}\,\text{s cm}^{-1}$.
(a)[3]
The loudspeaker sends out sound at a speed of $330\,\text{m s}^{-1}$. Determine the wavelength of the sound.
(b)[2]
The loudspeaker now travels in a straight line while still producing the same sound of constant frequency. The period of the trace on the CRO rises steadily. Describe the motion of the loudspeaker.
Worked solution & mark scheme
This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Period found by $T = 5.8 \times 5.0 \times 10^{-4} = 2.9 \times 10^{-3}\,\text{s}$” …