Question

Doppler Effect:

1. A stationary police officer using a speed “radar detector” sends a signal with a frequency of 100,000 Hz. The speed of sound is 340 m/s.

1. What is the wavelength of the (ultra) sound wave produced by the detector?
2. The sound wave reflects off a vehicle moving toward the officer. How does the frequency of the reflected sound wave (as recorded by the detector) compare to the original sound wave?

2. The light waves from a distance start appear to be “blue shifted”. Is the star moving toward or away from the earth? Explain your answer.

Answer 1

1 . Given that frequently f= 100000 Hz

Velocity of the wave v = 340 m/s

a. We have the relationship wavelength, d = v / f

So here wavelength of the sound = 340 / 100000

= 3.4 x 10 -3 metres

b .as the vecicle is moving towards the officer,

Due to dopler effect of sound waves, the detector will recieve a reflected sound which has a higher frequency as compared to the original sound wave.

2. A blue shift is a demonstration of shifting of the frequency of the oroginal lightwave towads a higher frequency . And as per dopler effect a shift to higher frequency ( blue shift) is shown by a source or star which is moving towards the observer. So the star is moving towards the earth.