Optics Question 148
Question: In hydrogen spectrum the wavelength of $ {H _{\alpha }} $ line is 656 nm whereas in the spectrum of a distant galaxy, $ {H _{\alpha }} $ line wavelength is 706 nm. Estimated speed of the galaxy with respect to earth is
[IIT-JEE 1999; UPSEAT 2003]
Options:
A) $ 2\times 10^{8}m/s $
B) $ 2\times 10^{7}m/s $
C) $ 2\times 10^{6}m/s $
D) $ 2\times 10^{5}m/s $
Show Answer
Answer:
Correct Answer: B
Solution:
$ v=\frac{c\Delta \lambda }{\lambda }=\frac{3\times 10^{8}\times (706-656)}{656}=\frac{1500}{656}\times 10^{7} $
$ =2\times 10^{7}m/s $
