Electromagnetic Technology

How do traffic lights at car intersections know when a vehicle is present?

Many traffic lights are triggered to change by the approach of a car. The principle is similar to the metal detector, in that there are coils of current-carrying wire just below the road where the vehicles stop at the intersection. When a large enough amount of metal passes over the coil, it induces a change in the current that creates a signal in the electronic circuits that control the traffic light.


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