Question

A car is driving at 10 m s−1 towards a stationary siren and flashing light. Explain, with a numerical justification, why the driver hears a different frequency sound from the siren compared to a stationary observer, whereas both see the same colour of flashing light

Answer 1

Given:

From given data the change of frequencies is due toDOPPLER EFFECT orDOPPLER SHIFT. doppler shift describes changes in frequency of any kind of light or sound waves produced by a moving source with respect to an observer, waves emitted by an object travelling toward get compressed while prompting a higher frequency as the source approaches the observer.

Sound waves emitted by siren spread out in a spherical wave, so the higher frequency is received by the car driving at 10ms-1  moving towards the source and lower frequency is received by the stationery observer who is away from siren.

The flash light of siren emits lowest frequency so the stationery observer and driver sees the same colour of flashlight . the apparent frequencyof the light they emit decreases and their colour will move towards the red end of the spectrum and it is called red shifting.