COIL, THE KING OF ELECTRICITY

We know electron whirls and spins in an atom. When an electron revolves, the electric fields also circulates. Consequently a magnetic field is created perpendicular to the plane of rotation(maxwell's equation).

Suppose in a loop of wire, a current (bunch of electrons) flows, a magnetic field will be created through the loop. One side north pole and the other side south pole. We will extend this principle further. If we have a coil of wire (more number of loops). The magnetic fields are added up and we get a strong magnetic field. In short, the current carrying coil acts like a bar magnet with north pole at one end and the south pole at the other end.

Now we will do a simple experiment to demonstrate magnetism created by a coil. Wire the circuit as given below.

Here, when the switch is closed, the current flows through the coil only. Current cannot pass through LED because it is a one way device. While the current flows through the coil, magnetic field builds up in the coil and reaches the saturation value.

Now open the switch, the battery is cut off. The magnetic field in the coil starts to collapse. The collapsing magnetic field creates opposite voltage, opposite current in the coil (Faraday's law).
Now the current flows through the LED and illuminates it for a brief time. This proves the creation and destruction of magnetism in the coil.

Applications: Microphone coverts voice into varying electric current. This current is amplified and fed into the speaker. The changing current pass through the coil in the speaker. Hence changing magnetic field is created in it. This causes coil to vibrate (Lawrence force). The attached diaphragm also vibrates producing loud sound (A simple explanation).

The coil is the main part in all the motors, meters, transformers, all electronic devices, house hold electrical devices etc. We know "coil winding" is a trade and educational course. So the simple coil of copper wire plays a major role in electrical engineering.

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