Electromagnetic Induction

What is electromagnetic induction?

When an alternative current is allowed to flow through a certain circuit and that circuit is kept near a neutral circuit, the former circuit induces charge distributions in the latter circuit resulting in an induced current in the latter circuit. This phenomenon is called the electromagnetic induction.

Thus a potential difference arises across the circuit when exposed to a varying magnetic field.

Faraday's law-

Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.

(Photo credit: gic-edu.com)

Thus, fluctuating magnetic fields cause currents to flow in conductors placed within them.

This is called induction because there is no physical connection between the conductor and the magnet. The current is said to be induced in the conductor by the magnetic field.

In order to produce the maximum force needed for induction, usually the conducting wire is kept perpendicular to the magnetic lines of force.

The direction that the induced current flows is found using the direction of the lines of force and by the direction the wire is moving in the field.

Faraday's experiment:

Faraday's experiment can mainly be discussed under two sub topics:
1. When a magnet is moving in and out of a stationary loop
2. Using two coils (Primary coil and secondary coil)

Method 1:

Magnet moving towards the coil and out of the coil. The deflection of the needle is proportional to the speed at which the magnet is moved.

(Photo credit: exchange.smarttech.com )

In the experiment above, a known pole (North or South) of the magnet is moved towards the coil, a deflection in the needle of the galvanometer can be seen.

When we change the pole and move towards the coil, the galvanometer deflects in the opposite direction to the direction in which it deflected in the previous occasion.

(Photo credit: www.mitshubishielectric.com)

When we move the magnet away from the coil, the deflection of the needle is in the opposite direction to the direction in which the magnet was moved towards the magnet, while facing the same pole towards the coil.

When we move the magnet towards the coil and keep the coil stationary for some time, the needle achieves 0 current position.

Furthermore, faster we move the magnet towards or out of the coil, faster will be the deflection of the magnet.

(Photo credit: frazerphysics.blogspot.com )

Method 2:

In this method let us replace the magnet of the previous experiment with a current carrying coil and expect to observe the effects as current carrying coil produces magnetic field.

(Photo credit: physicsanalyst.com)

When the primary coil (P) is completed by turning on the switch, current flows through P. At some time, an induced current as explained above starts to flow through the secondary coil (S).

When P is completed the galvanometer deflects to a certain direction (depends upon the direction of current in P). When P is incomplete or when the switch in P is turned off, the needle of the galvanometer deflects in the opposite direction and achieves zero current configuration.

Action of a transistor

In this note I will present details only about the npn transistor. For those who are interested only on the pnp transistor, you can switch the action of the npn transistor and the behavior of current to adjust with the characteristics of the pnp transistor. (Photo credit: mahasona10000.blogspot.com ) As in the case of a p-n junction,the two n parts of the npn transistor contain an excess of free electrons. In contrast, the p part contains excess holes. As in the case of the p-n junction, in the npn transistor depletion regions develop and junction barriers occur. (Photo credit: daenotes.com) For the correct functioning of the transistor, the first p-n junction is forward biased and the second p-n junction is reverse biased. This results for the first p-n junction to be of low resistance and the second p-n junction to be of high resistance. (Photo credit: www.nzart.org.nz ) The letters of these elements

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