Write a note a transformers.

Explanation

A transformer is a device used for varying AC voltages. It works on the principle of mutual induction.
When electrical power is transmitted over long distances, it is economical to transmit power at a high voltage and low current in order to minimise the loss due to heating effect of the electric current. So the voltage is stepped up at a generating station. At the receiving end the AC must be at a low voltage so as to operate various electrical appliances. Hence voltage is stepped down at the receiving end.
A transformer consists of two coils called primary P and secondary S, wound on the same laminated soft iron core. The alternating emf to be stepped up or stepped down is applied to the primary coil and the output of the altered emf is obtained across the secondary.
Working: As the current through the primary varies, the magnetic flux linked with the secondary also varies. As a result, alternating emf of the same frequency is induced across the secondary. The magnitude of the induced voltage in the secondary, depends on the voltage across primary. If `V_(P)andV_(S)` are the input and output voltages respectively and `N_(P)andN_(S)` are the number of turns in the primary and secondary respectively then
`(V_(s))/(V_(P))=(N_(S))/(N_(P))=T` (turns ratio)
Power output = Power input
`V_(S)I_(S)=V_(P)I_(P)`
i.e., `(V_(S))/(V_(P))=(I_(P))/(I_(S))`,
For practical transformer, efficiency `eta=(V_(S)I_(S))/(V_(P)I_(P))lt1`
Source of energy loss in transformers are due to (i) copper loss (ii) magnetic flux linkage loss, (iii) hysteresis loss and (iv) eddy current loss.