Single correct option
When a source of sound moves towards a stationary listener, the pitch of the sound heard by the listener
- A. decreases, as the apparent frequency is lower
- B. remains the same, as the source frequency does not change
- C. increases, as the apparent frequency is higher
- D. increases, as the speed of sound in air increases
Show answer and solution
Answer: (C) increases, as the apparent frequency is higher
This is the Doppler effect. As the source approaches, successive wavefronts are emitted closer together, so the listener receives more waves per second and perceives a higher frequency. The speed of sound is fixed by the medium and does not change with source motion, hence the last option is wrong. When the source recedes, the pitch falls.
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