Problem 5.

Light of wavelength 497.0 nm appers to have a wavelength of 500.2 nm when it reaches eart from a distance star. find the velocity of the star if the speed of light is 300000000 m/s.

Solution:

In this problem we need to use the expression for the Doppler shift of the frequency of the wave for an observer moving relative to the source of the waves.. If the source of the light (wave) is moving with a speed then the change in the frequency is

where is the speed of light. Since

Then

and

From this expression we can find the speed of the source