A transformer is a device used to convert low a.c. voltage into high a.c. voltage and vice versa. It is of two types: -
A step-up transformer converts low a.c. voltage into high a.c voltage and step-down transformer converts high a.c. voltage into low a.c voltage. The instrument is based on the principle of mutual induction.
Structure: It consists of a rectangular soft iron core made up of laminated sheets. There are two coils which are not connected to one another in any way. These coils are wound on the iron core. One of the coils may be connected to a source of a.c. This coil is called primary coil and the other is called secondary coil.
The e.m.f. of a.c. source applied across the primary coil is called input voltage and e.m.f. induced across the secondary coil is called output voltage.
Principle: When an alternating e.m.f. is applied to the primary coil, a changing current flowing in it produces an alternating magnetic flux in it. This causes to change the magnetic flux linked with the secondary coil. An alternating e.m.f. is then induced in the secondary coil. It is called principle of mutual induction on which transformers are based.
The formula showing the relation between the primary voltage and secondary voltage is as follows: -
Transformer is needed during the both cases, either to increase the voltage or to decrease it. Without transformer no change in the voltage of alternating current can be made. That's why the use of alternating current is limited without transformer.
|Step-up transformer||Step-down transformer|
|It increases the output electricity more than input electricity.||It decreases the output electricity more than input electricity.|
|It increases the magnitude of AC emf.||It decreases the magnitude of AC emf.|
Power of a bulb (P) = 100 W
Potential difference (V) = 220 V
Current electricity (I) = 5 Ampere
According to the formula,
P = V × I
or,100 × X = 220 × 5
© 2019-20 Kullabs. All Rights Reserved.