IB Physics SL C 5 1 Doppler Effect Questions

Explain the Doppler effect and use relative source-observer motion to analyse observed frequency, wavelength, wavefronts and red-shift.

Exam points

define the Doppler effect as a change in observed frequency caused by relative motion between a source and an observer
explain how source or observer motion changes wavefront spacing and observed frequency while wave speed in the medium remains fixed
interpret Doppler frequency shifts using source-observer direction, closest approach, wavefront diagrams and time graphs, including sound and red-shift evidence

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Study C.5.1—Doppler effect conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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This question is about the Doppler effect.

Georgia carries out an experiment to measure the speed of mosquitoes. She sets up a microphone to record the sounds of passing mosquitoes.

Figure for Question IB Physics SL C 5 1 Doppler Effect Questions question 1 — IB Physics SL

One mosquito is moving in a straight line with constant speed and passes very close to the microphone as seen in the diagram. The mosquito produces a sound of constant frequency. The speed of sound in air is $340 \mathrm{~m} \mathrm{~s}^{-1}$ .

The maximum frequency recorded is 751 Hz and the minimum frequency recorded is 749 Hz . Explain this observation.

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IB Physics SL C 5 1 Doppler Effect Questions question 1