The radar used by police to check over-speeding vehicles works on the principle of
Raman effect
Induction effect
Doppler effect
Coulomb effect
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This question was previously asked in
UPSC CAPF – 2020
The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. Police radar guns emit radio waves towards a moving vehicle. When these waves reflect off the vehicle, their frequency is shifted. If the vehicle is moving towards the radar, the reflected waves have a higher frequency; if moving away, they have a lower frequency. The radar unit measures this frequency shift and calculates the vehicle’s speed based on the magnitude of the shift.