Q. In H spectrum, the wavelength of $H_{\alpha}$ line is 656 nm whereas in a distance galaxy, the wavelength of $H_{\alpha}$ line is 706 nm. Estimate the speed of galaxy with respect to earth
A) $2 \times 10^{8}ms^{- 1}$
B) $2 \times 10^{7}ms^{- 1}$
C) $2 \times 10^{6}ms^{- 1}$
D) $2 \times 10^{5}ms^{- 1}$
Explanation
(b) $\mathrm{\Delta}\lambda = 706 - 656 = 50\ nm = 50 \times 10^{- 9}m,v = ?$
As $\frac{\mathrm{\Delta}\lambda}{\lambda} = \frac{v}{c}$
$\therefore\ v = \frac{\mathrm{\Delta}\lambda}{\lambda} \times c = \frac{50 \times 10^{- 9}}{656 \times 10^{- 9}} \times 3 \times 10^{8}$
$= 2.2 \times 10^{7}ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.