Statement:
The frequency change of light waves when there is relative motion between the source of light and observer is called Doppler effect in light.
Explanation:
i. Consider a source of light ‘S’ moving relative to observer 1 and 2.
ii. When the source of light ‘S’ moves towards observer 1 and away from observer 2, the wavelength of light appears to be less to observer 1 and more to the observer 2.
iii. The apparent frequency of light as perceived by an observer is given by
where v0 is the actual frequency of light, v is the frequency of light as measured by the observer.
v. = radial component of velocity of source relative to the observer.
c = speed of light in vacuum.
iv. When v << c, then equation (1) can be written as,
v. The negative sign is used in equation (2) when the source moves away from the observer and we substitute the magnitude of v. Similarly, (+) sign is used when the source moves towards the observer and we substitute the magnitude of v.
vi. The equation in terms of wavelength is given by,
In equation (3), we use the positive sign when the source moves away from the observer and we put the magnitude of v, Similarly, when the source moves towards the observer, (–) sign and magnitude of v is used.
