Optics Question 189
Question: The k line of singly ionised calcium has a wavelength of 393.3 nm as measured on earth. In the spectrum of one of the observed galaxies, this spectral line is located at 401.8 nm. The speed with which the galaxy is moving away from us, will be
[Pb. PET 2003]
Options:
A) 6480 km/s
B) 3240 km/s
C) 4240 km/sec
D) None of these
Show Answer
Answer:
Correct Answer: A
Solution:
$ \frac{\Delta \lambda }{\lambda }=\frac{v}{c} $
Therefore $ \frac{(401.8-393.3)}{393.3}=\frac{v}{3\times 10^{8}} $
Therefore v = 6.48 x106 m/s = 6480 km/sec.
