Optics Question 242

Question: The apparent wavelength of the light from a star moving away from the earth is 0.01% more than its real wavelength. Then the velocity of star is

[CPMT 1979]

Options:

A) 60 km/sec

B) 15 km/sec

C) 150 km/sec

D) 30 km/sec

Show Answer

Answer:

Correct Answer: D

Solution:

$ \frac{\Delta \lambda }{\lambda }=\frac{v}{c}\Rightarrow v=\frac{c}{\lambda }\Delta \lambda =\frac{c}{\lambda }(\lambda ‘-\lambda )=c\times \frac{0.01}{100} $

$ =3\times 10^{4}m/s=30\ km/\sec $



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