What is dopler effect

Doppler’s effect

• Doppler Effect is the shift in frequency of light when there is relative motion between the source and observer.
• It is used to measure the speed of a receding object.
• When the source is moving away from the observer then the wavefronts have to travel a greater distance to reach the observer.
• When a star is moving away from the earth the wavelength in the middle of the visible region of the spectrum moves towards the red end of the spectrum.
• As a result star looks more reddish when moves away from the earth.
• This is known as red shift phenomenon.
• When the waves are received from a sourcemoving towards the observer, there is an apparent decrease in wavelength. This is called blue shift.
• The fractional change in frequency (Δν/ν)=(–v_radial/c),
• Where v_radial= component of the source velocity along the line joining the
• observer to the source; v_radial is considered positive when the source moves away from the observer.
• Thus, the Doppler shift can be expressed as:
• (Δν/ν) = (–v_radial/c);
• It is valid when the speed of the source is small compared to that of light.