Question: The apparent wavelength of the light from a star moving away from the earth is 0.01% more than its r...

Question

The apparent wavelength of the light from a star moving away from the earth is 0.01% more than its real wavelength. Then the velocity of star is.

Answer 1

Solution

$\frac{\Delta\lambda}{\lambda} = \frac{v}{c} \Rightarrow v = \frac{c}{\lambda}\Delta\lambda = \frac{c}{\lambda}(\lambda' - \lambda) = c \times \frac{0.01}{100}$

$= 3 \times 10^{4}m/s = 30\mspace{6mu} km/\sec$