The Doppler Effect
2 marks · NormalGive one everyday example of the Doppler effect with sound, and briefly explain how it is noticed.
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Example: An ambulance siren sounds higher in pitch as it approaches and lower as it moves away; this is noticed as the apparent frequency changes with the movement.
Also accept: Police car/Fire engine, motorbike passing with a change in siren pitch as it passes by.; Formula One car passing the pit lane as its engine's sound pitch changes.
Common mistakes: Not explaining how the effect is noticed.; Describing a stationary source.
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Marking points
B1 · 1 mark · Valid everyday example given (e.g. siren, car passing).
B2 · 1 mark · Explanation of higher frequency as it approaches and lower as it recedes, or equivalent.
Worked solution
Example: An ambulance with its siren sounding. As the ambulance approaches, the pitch of the siren is higher; as it moves away, the pitch is lower. This is due to the Doppler effect.