Question

When the police want to know how fast your car is going, they shoot a "radar gun" at the car. The radar gun emits waves at approximately 24.15 GHz. Those waves reflect off of your car and are detected by the same "radar gun" that emitted them. The detector can detect both frequency and intensity. Using concepts of general physics, explain how the radar gun works. You probably want to draw pictures, use an equation or two, and use words.

Answer 1

radar guns used by police to identify and catch speeding cars. Because radar devices used by police cast a wide net of radio waves but only track one specific target, radar detectors in moving cars often pick up on radar radio waves before the car comes within close enough range of the police car to be tracked.

Speed guns use Doppler radar to perform speed measurements.When the object is approaching the radar, the frequency of the return waves is higher than the transmitted waves; when the object is moving away, the frequency is lower. From that difference, the radar speed gun can calculate the speed of the object from which the waves have been bounced. This speed is given by the following equation:

v=(Δf/f)x(c/2)

where Δf is the difference in frequency between the radio waves that are emitted and those received back by the gun, f is the emitted frequency of the radio waves and c is the speed of light.