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An observer moves toward a stationary source of sound with a speed 1/5th of the speed of sound. The wavelength and frequency of the sound emitted are λ and f respectively. The apparent frequency and wavelength recorded by the observer are respectively:

1. 0.8f, 0.8λ
2. 1.2f, 1.2λ
3. 1.2f, λ
4. f, 1.2λ

Correct answer: 1.2f, λ

Solution

When the observer moves toward the stationary source, the apparent frequency increases due to the Doppler effect, but the wavelength remains unchanged as the source is stationary. The apparent frequency is given by f' = f(1 + v_observer/v_sound), which results in 1.2f, while the wavelength remains λ.

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