Q. 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
A) $2 \times 10^{8}m/s$
B) $2 \times 10^{7}m/s$
C) $2 \times 10^{6}m/s$
D) $2 \times 10^{5}m/s$
Explanation
(b) $v = \frac{c\mathrm{\Delta}\lambda}{\lambda} = \frac{3 \times 10^{8} \times (706 - 656)}{656} = \frac{1500}{656} \times 10^{7}$
$= 2 \times 10^{7}m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.