IB Physics SL C.5.1 Doppler Effect

Practise explaining the Doppler effect through changing wavefront spacing and predicting observed frequency or wavelength when a source and observer approach or recede.

Exam points

explain compressed wavefronts ahead of an approaching source and stretched wavefronts behind it
predict frequency increase on approach and decrease on recession, with the opposite wavelength trend
distinguish a change in observed frequency from a change in the source's emitted frequency

[Maximum number: 2]

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 C.5.1—Doppler effect 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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C.5.1—Doppler effect question 1