Chapter 11, Problem 11TE

If your metal car moves over a wide, closed loop of wire embedded in a road surface, will the magnetic field of the Earth within the loop be altered? Will this produce a current pulse? Can you think of a practical application for this at a traffic intersection?

To determine

Whether there would be variation in the Earth’s magnetic field within a wire loop due to the motion of a car through it, whether an electric pulse would be generated by it and its applications.

Answer to Problem 11TE

There would be variation in the Earth’s magnetic field within a wire loop due to the motion of a car through it and an electric pulse would be generated by it. This can be used at road intersections and traffic signals as a vehicle detector.

Explanation of Solution

A car is made of metal. The Earth’s magnetic field converges when it passes close to the vehicle. Therefore, it increases the magnitude of the magnetic field nearby. The car passes through the wire loop on the road, and the magnetic flux associated with the loop changes with time. A time changing magnetic flux produces an emf along the loop according to the Faraday’s Law of induction. This creates an impulse of electric current along the loop.

There is a production of an electric impulse when a car passes through the loop. This can be used to build a triggering automobile traffic light. It happens several times that no vehicle is present at the signal, and still, one car is waiting for the traffic light to go green. In this case, the device can be installed, which can detect the number of the car in the lanes, and depending upon these numbers, traffic light can change. Also, a device can be built to count the number of cars passing through roads. This can help people to check the traffic on the road.

Conclusion:

Therefore, there would be variation in the Earth’s magnetic field within a wire loop due to the motion of a car through it and an electric pulse would be generated by it. This can be used at road intersections and traffic signals as a vehicle detector.