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 $



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