Waves - Result Question 75
77. An observer moves towards a stationary source of sound with a speed $1 / 5$ th of the speed of sound. The wavelength and frequency of the sound emitted are $\lambda$ and $f$ respectively. The apparent frequency and wavelength recorded by the observer are respectively.
[2003]
(a) $0.8 f, 0.8 \lambda$
(b) $1.2 f, 1.2 \lambda$
(c) $1.2 f, \lambda$
(d) $f, 1.2 \lambda$
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Answer:
Correct Answer: 77. (c)
Solution:
- (c) Wavelength remains constant (unchanged) in this case.
$ f _{\text{apparent }}=(\frac{u+u / 5}{u}) f=\frac{6}{5} f=1.2 f $
