Q. The observed wavelength of light coming from a distant galaxy is found to be increased by 0.5% as compared with that coming from a terrestrial source. The galaxy is
A) Stationary with respect to the earth
B) Approaching the earth with velocity of light
C) Receding from the earth with the velocity of light
D) Receding from the earth with a velocity equal to $1.5 \times 10^{6}m/s$
Explanation
(d) $\frac{\Delta\lambda}{\lambda} = \frac{v}{c}$, Now $\Delta\lambda = \frac{0.5}{100}\lambda \Rightarrow \frac{\Delta\lambda}{\lambda} = \frac{0.5}{100}$
$\therefore v = \frac{0.5}{100} \times c = \frac{0.5}{100} \times 3 \times 10^{8} = 1.5 \times 10^{6}m/s$
Increase in $\lambda$ indicates that the star is receding
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.