A physicist drives through a stop light. When he is pulled over, he tells the police officer that the Doppler shift made the red light of wavelength 660 nm appear green to him, with a wavelength of 555 nm. The police officer writes out a traffic citation for speeding. How fast was the physicist traveling, according to his own testimony?

Speed of physicist car is 0.036c or 1.08 x 10⁷ m/s .

Explanation:

Doppler Effect is defined as the change in frequency or wavelength of the wave as the source or/and observer moving away or towards each other.

In this case, the Doppler effect equation in terms of wavelength is :

      ......(1)

Here is source wavelength, is observed wavelength, v is speed of the observer and c is the speed of light.

Given :

Source wavelength, = 660 nm = 660 x 10⁻⁹ m

Observed wavelength, = 555 nm = 555 x 10⁻⁹ m

Substitute these values in the equation (1).

v = 1.08 x 10⁷ m/s