Question

A star is moving away from the Earth with speed $V$. Change in wavelength $(d\lambda)$ observed on Earth is

• A. $\frac{\lambda V}{C}$
• B. $\frac{\lambda V}{(C + V)}$
• C. $\frac{\lambda C}{(C + V)}$
• D. $\frac{\lambda C}{V}$

Answer 1

Answer: (A)

$\frac{\lambda V}{C}$

Answer 2

Doppler shift in wavelength of the light source is given by
$\Delta \lambda = \frac{V \lambda }{C}$
For motion away from earth $d \lambda$ is positive .