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 $
