Q. The fractional change in wavelength of light coming from a star is 0.014% what is its velocity?
A) $42 \times 10^{3}ms^{- 1}$
B) $3.8 \times 10^{8}ms^{- 1}$
C) $3.5 \times 10^{3}ms^{- 1}$
D) $4.2 \times 10^{4}ms^{- 1}$
Explanation
(d) The doppler’s wavelength shift is given by
$\frac{\mathrm{\Delta}\lambda}{\lambda} = \frac{v}{c}$
Where, v is velocity and c is speed of light.
Given,
$\frac{\Delta\lambda}{\lambda} = 0.014\%,\ \ c = 3 \times 10^{8}ms^{- 1}$
$\Longrightarrow v = \frac{\mathrm{\Delta}\lambda}{\lambda} \times c = \frac{0.014}{100} \times 3 \times 10^{8}$
$= 4.2 \times 10^{4}ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.