The Doppler Effect
3 marks · NormalDescribe a practical experiment you could carry out to demonstrate the Doppler effect using sound.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Tie a small sound source (e.g. buzzer) to a string and swing it in a circle. A stationary observer hears the pitch change as the source moves towards and away from them, demonstrating the Doppler effect.
Also accept: Move a speaker rapidly past a stationary observer and listen for the change in pitch.; Use a toy car with sound source moving past observer.
Common mistakes: Describing a setup without moving sound source.; Leaving out observer's experience.
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Describes moving sound source (e.g., buzzer on string, speaker, toy car).
M2 · 1 mark · Stationary observer listens for change in pitch/frequency.
A1 · 1 mark · States that frequency increases as source approaches, decreases as it moves away (or mentions pitch change).
Worked solution
Tie a small buzzer that emits a steady sound to a length of string. Swing the buzzer in a circle at arm's length. A person standing nearby will hear the pitch of the buzzer rise and fall as it moves towards and away from them, demonstrating the Doppler effect.