What is Doppler effect of sound? Derive expression for apparent frequency of sound. When source is moving away from stationary listener.

What is Doppler effect in light? Write the expression for Doppler shift.

A source of sound is moving with a velocity of 50ms^(-1) towards a stationary observer . The Observer measure the frequency of sound as 500Hz. The appartment frequency of sound as heard by the observer when source is moving away from hom with the same speed is (Speed of sound at room temperature 350ms^(-1)