When source of sound moves towards a stationary observer, the apparent frequency heard by him (a) increases and wavelength also increases. (b) increases while wavelength decreases. (c) remains the same while wavelength decreases. (d) decreases and wavelength remains the same.

Answer: (b). A moving source crowds its waves together in front: λ' = (v - vs)/(n), smaller than λ. With the speed of sound unchanged, n' = (v)/(λ') is larger. So the answer is (b): frequency increases while wavelength decreases.

When source of sound moves towards a stationary observer, the… | MHT CET 2025 (19 Apr, Shift 1)

Q11MHT CET 2025 · 19 APR · SHIFT 1Easy

Doppler Effect

When source of sound moves towards a stationary observer, the apparent frequency heard by him

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Answer: (b)

A moving source crowds its waves together in front: $\lambda' = \frac{v - v_s}{n}$ , smaller than $\lambda$ .
With the speed of sound unchanged, $n' = \frac{v}{\lambda'}$ is larger.
So the answer is (b): frequency increases while wavelength decreases.

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Doppler Effect question from MHT CET 2025 (19 Apr, Shift 1)

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