MODEL RELEASED. Radar speed gun. A policeman uses a radar speed gun to see whether drivers are keeping within the local speed limit. When this gun is pointed at a moving object it displays the speed in kilometres per hour on a small screen on the back of the gun. The device works by bouncing a radar beam off the vehicle and comparing the frequency of the reflected signal to that of the initial output. Due to the doppler effect,the reflected frequency is lowered by a factor that depends on the speed of the moving object. The same effect is responsible for the sudden drop in the pitch of a siren when an ambulance passes a stationary observer | |
Licence : | Droits gérés |
Crédit: | Science Photo Library / Hart-Davis, Adam |
Taille de l’image : | 3401 px × 2346 px |
Model Release : | Disponible |
Property Release : | Non requis |
Restrictions : | - |