Optics Question 254
Question: In the spectrum of light of a luminous heavenly body the wavelength of a spectral line is measured to be 4747 Å while actual wavelength of the line is 4700 Å. The relative velocity of the heavenly body with respect to earth will be (velocity of light is $ 3\times 10^{8}m/s $ )
[MP PMT/PET 1998]
Options:
A) $ 3\times 10^{5}m/s $ moving towards the earth
B) $ 3\times 10^{5}m/s $ moving away from the earth
C) $ 3\times 10^{6}m/s $ moving towards the earth
D) $ 3\times 10^{6}m/s $ moving away from the earth
Show Answer
Answer:
Correct Answer: D
Solution:
$ \Delta \lambda =\frac{v _{s}}{c}\lambda \Rightarrow v _{s}=\frac{\Delta \lambda .c}{\lambda }=\frac{47\times 3\times 10^{8}}{4700} $
$ =3\times 10^{6}m/s $ away from earth
