AIIMS 2018 Physics Doppler Effect MCQ Question
A source producing sound of frequency 170 Hz is approaching a stationary observer with a velocity of 17 m/s. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air = 340 m/s)
0.1 m
0.2 m
0.4 m
0.5 m
Correct Answer
Detailed Explanation
When a source of sound approaches a stationary observer, the observed frequency increases due to the Doppler effect. The apparent wavelength (λ') can be calculated using the formula λ' = v/f', where v is the speed of sound (340 m/s) and f' is the observed frequency, which can be found using f' = f(v/(v - vs)), where f is the source frequency (170 Hz) and vs is the source velocity (17 m/s). This results in an observed frequency of 200 Hz, leading to a new wavelength of 1.7 m, and the change in wavelength is 0.1 m (from 2 m to 1.9 m), making option A correct. Other options are incorrect as they do not accurately reflect the calculated change in wavelength based on the Doppler effect.
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