When an automobile moves over a wide, closed loop of wire embedded in a road surface, is the magnetic field of the Earth within the loop altered? Is a pulse of current produced? Can you cite a practical application for this at a traffic intersection?

Answer 1

There is a redistribution of the Earth's feld lines due to the steel in the car. This causes the flux through the wired to change and a small emf to be generated. This can cause a pulse of current to flow. This can be amplified to detect the presence of the car. This can be used at intersections to activate green lights and determine the length of time that the light remains green.

Small vehicles like bicycles and motor scooters often do not activate such detectors. This can cause long waits at intersections with not much car traffic.

I hate it when that happens.