Optics Question 235
Question: The observed wavelength of light coming from a distant galaxy is found to be increased by 0.5% as compared with that coming from a terrestrial source. The galaxy is
[MP PMT 1993, 2003]
Options:
A) Stationary with respect to the earth
B) Approaching the earth with velocity of light
C) Receding from the earth with the velocity of light
D) Receding from the earth with a velocity equal to $ 1.5\times 10^{6}m/s $
Show Answer
Answer:
Correct Answer: D
Solution:
$ \frac{\Delta \lambda }{\lambda }=\frac{v}{c}, $ Now $ \Delta \lambda =\frac{0.5}{100}\lambda \Rightarrow \frac{\Delta \lambda }{\lambda }=\frac{0.5}{100} $
$ \therefore v=\frac{0.5}{100}\times c=\frac{0.5}{100}\times 3\times 10^{8}=1.5\times 10^{6}m/s $ Increase in l indicates that the star is receding.
