Optics Question 255
Question: The wavelength of light observed on the earth, from a moving star is found to decrease by 0.05%. Relative to the earth the star is
[MP PMT/PET 1998]
Options:
A) Moving away with a velocity of $ 1.5\times 10^{5}m/s $
B) Coming closer with a velocity of $ 1.5\times 10^{5}m/s $
C) Moving away with a velocity of $ 1.5\times 10^{4}m/s $
D) Coming closer with a velocity of $ 1.5\times 10^{4}m/s $
Show Answer
Answer:
Correct Answer: B
Solution:
$ \frac{\Delta \lambda }{\lambda }=\frac{v}{c}\Rightarrow \frac{0.05}{100}=\frac{v}{3\times 10^{8}} $
Therefore v = 1.5 x 105 m/s (Since wavelength is decreasing, so star coming closer)
