The radar gun of a police car emits an electromagnetic wave with a frequency of

Question

The radar gun of a police car emits an electromagnetic wave with a frequency of 7.0 times 10^9 Hz. The approach is essentially head on. The wave from the gun reflects from the speeding car and returns to the police car, where on-board equipment measures its frequency to be greater than the emitted wave by 2100 Hz. Find the speed of the car with respect to the highway. The police car is parked. Random polarized light of intensity I_0 is passed through three polarizer, The last two (2^nd and 3^rd) are rotated by 36 and 23 degree respectively. By what factor the light intensity has been reduced by during this process? 69 percentage 39 percentage 31 percentage 50 percentage 0.0 percentage

Explanation / Answer

f = fo fs

f = fo[1+v/c]-fs

= [fs(1+v/c)](1+v/s) - fs

= fs[1+2v/c + v^2/c^2] - fs

= fs[(1+2v/c +v^2/c^2) - 1]

= fs(2v/c + v^2/c^2)

v/c << 1 --> f = fs*2v/c

v = c*f/2*fc

v = (3.00*10^8 m/s) *[2100 Hz / (2*7.0*10^9 Hz)]

= 45 m/s

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