A motorist, who had driven through a red traffic light, is stopped by police. When…
PHYSICS · Subjective · A Level · Physics · Particles and radiation · Particles and radiation
Problem
A motorist, who had driven through a red traffic light, is stopped by police. When questioned, the motorist tells the police that, because of the Doppler effect, he saw the light to be amber-coloured, and so he could drive through the traffic lights legally. The police officer charges the motorist for speeding and reckless driving. If the shortest wavelength of red light is 620 nm and the longest wavelength of amber light is 590 nm, explain, with the use of a Doppler effect calculation, why the policeman charges the motorist.
(Take the speed of light in air to be 3.0×108 ms−1 .)