Optics Question 260

Question: A rocket is going away from the earth at a speed 0.2c, where c = speed of light. It emits a signal of frequency $ 4\times 10^{7}Hz $ . What will be the frequency observed by an observer on the earth

[RPMT 1996]

Options:

A) $ 4\times 10^{6}Hz $

B) $ 3.2\times 10^{7}Hz $

C) $ 3\times 10^{6}Hz $

D) $ 5\times 10^{7}Hz $

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Answer:

Correct Answer: B

Solution:

$ \nu ‘=\nu ( 1-\frac{v}{c} )=4\times 10^{7}( 1-\frac{0.2c}{c} )=3.2\times 10^{7}Hz $



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