2020 · Q5
The radar used by police to check over-speeding vehicle works on the principle of
general-sciencephysics-light-electricity
- ARaman effect
- BInduction effect
- CDoppler effect
- DCoulomb effect
Explanation
Police speed radar transmits microwaves toward a vehicle and measures the frequency shift of the reflected waves — the Doppler effect: waves returning from an approaching vehicle are shifted to higher frequency in proportion to its speed. The Raman effect concerns inelastic scattering of light, electromagnetic induction concerns induced emf, and Coulomb's law concerns electrostatic force — none of them measures speed.