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# Transformer

Transformer is a device used for converting low voltage into high voltage and high voltage into low voltage. It works on the principle of electromagnetic induction.

Transformer

Transformer is a device used for converting low voltage into high voltage and high voltage into low voltage. It works on the principle of electromagnetic induction. It consists of primary and secondary coil insulated from each other. In Figure 3.26, the alternating current owing through the primary coil induces magnetic field in the iron ring. The magnetic field of the iron ring induces a varying emf in the secondary coil. Depending upon the number of turns in the primary and secondary coils, we can step-up or step-down the voltage in the secondary coil as shown in Figure 3.27. Step up transformer: The transformer used to change a low alternative voltage to a high alternating voltage is called a step up transformer. ie (Vs > Vp) . In a step up transformer, the number of turns in the secondary coil is more than the number of turns in the primary coil (Ns > Np).

Step down transformer: e transformer used to change a high alternating voltage to a low alternating voltage is called a step down transformer (Vs < Vp). In a step down transformer, the number of turns in the secondary coils are less than the number of turns in the primary coil (Ns < Np).

The formulae pertaining to the transformers are given in the following equations. A transformer cannot be used with the direct current (DC) source because of current in primary coil is constant (ie. DC). Then there will be no change in the number of magnetic field lines linked with the secondary coil and hence no emf will be induced in the secondary coil.

### Exercise 3

The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a 220 V ac supply. What will be the output voltage?

### Solution:

In a transformer, Es / Ep = Ns / Np

Es = Ns / Np x Ep

= 8/800 x 220

= 220/100

Es = 2.2 volt

### Exercise 4

A transformer is designed to give a supply of 8 V to ring a house bell from 240 V ac mains. The primary coil has 4800 turns. How many turns will be in the secondary coil.

### Solution:

In a transformer, Es / Ep = Ns / Np

Ns = Es / Ep x Np

= 8/240 x 4800

Ns = 4800/30 = 160 turns

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9th Science : Magnetism and Electromagnetism : Transformer |