Work Step by Step
The Earth’s magnetic field within the embedded loop does not change, but the magnetic field within the loop does change due to the car’s movement. A pulse is produced. This could be used to detect when cars are waiting in the left-hand turn lane, and trigger the left-turn arrow on the traffic light. Consider the wide loop of wire embedded in the road. When the iron chassis of a car passes over the loop, that will momentarily change the strength of the magnetic field in the loop. The law of electromagnetic induction tells us that a pulse of voltage will be induced in the loop, which induces a current.