MUTUAL INDUCTION | TRANSFORMER

What is Mutual Induction?

 MUTUAL INDUCTION: The phenomena of production of induced current in a coil due to change of current in a neighboring coil is called Mutual Induction.

 Suppose a system of two coil A and B placed close to each other. The coil A is connected to a battery and a switch, while a sensitive galvanometer is connected to the coil B. We observes as soon as the switch of a coil A is closed, the galvanometer shows a momentary deflection.

MUTUAL INDUCTION

 Similarly when the switch is opened, the galvanometer again shows a deflection but this time it's direction is opposite to that of the previous case.

We can explain these observations using Faraday's Law of electromagnetic induction. When the switch of coil A is closed, a current begin to flow in the coil due to which magnetic field is developed across the coil. Some of the magnetic lines of force this field start passing through the coil B. Since current is changing in the coil A, hence number of magnetic lines of force across the coil B also change due to which the current induced in the coil A becomes steady, number of magnetic lines of force across the coil A also becomes constant. Therefore, there is no more change in number of magnetic lines of force through the coil B due to which induced current in coil B reduces to zero.

Similarly when the switch of the coil A is opened, the flow of current through it stop and its magnetic field reaches to zero. The number of magnetic lines of force through the coil B decreases to zero due to which current is again induced in it but in opposite direction to that in the previous case.

 What is Transformer?

 The transformer is a practical application of mutual induction Transformer is used to increase or decrease AC voltages. Usage of transformer is common because they change voltages with relative little loos of energy. In fact, many of the devises in our homes, such as game systems, printers and stereos use transformer for their working.

Working of Transformer

A transformer has two coils, electrically insulated from each other, but wound around the same iron core. One coil is called Primary Coil. The other one is called Secondary Coil. Number of turns on the primary and the secondary coil are represented By Np and Ns respectively.

When primary coil is connected to a source of AC voltage, the changing current creates a changing in a magnetic field, which is carried through the core to the secondary coil.In the secondary coil, the changing field induces an alternating e.m.f.

The e.m.f. induced in the secondary coil, called the secondary Voltages Vs is proportional to the primary voltages Vp. The secondary voltages also depends on the ratio of the number of turns on the secondary coil to the number of turns on the primary coil, as shown by the following expression:

     

                                                           Vs / Vp = Ns / Np

If the secondary voltages is large then the primary voltages, the transformer is called Step-up Transformer. If the secondary voltage is smaller than the primary voltage, the transformer is called Step-up Transformer. In an ideal transformer, the electric power delivered to the secondary circuit is equal to the power supplied to the primary circuit.

        

                                                           Pp = Ps

                                                       Vp Ip = Vs Is