Question

What is the principle of transformer ? Explain the working of step-up transformer by drawing circuit diagram.

Hint:

The key relationship for an ideal transformer is \( \frac{V_s}{V_p} = \frac{I_p}{I_s} = \frac{N_s}{N_p} \). For a step-up transformer, \( N_s>N_p \), so voltage is increased and current is decreased. For a step-down transformer, \( N_s<N_p \), so voltage is decreased and current is increased.

Answer 1

Step 1: Principle of a Transformer: 
A transformer works on the principle of mutual induction. This principle states that when a changing current flows through one coil (the primary coil), it produces a changing magnetic flux in the space around it. If another coil (the secondary coil) is placed in this changing magnetic field, an electromotive force (e.m.f.) is induced across the secondary coil. 
Step 2: Working of a Step-Up Transformer: 
A step-up transformer is a device used to convert a low alternating voltage into a high alternating voltage. 
Construction: It consists of two coils, a primary coil (P) and a secondary coil (S), wound on a common laminated soft iron core. For a step-up transformer, the number of turns in the secondary coil (\(N_s\)) is greater than the number of turns in the primary coil (\(N_p\)).
Working:
An alternating voltage source (\(V_p\)) is connected across the primary coil. This causes an alternating current to flow through it.
This alternating current produces a continuously changing magnetic flux in the soft iron core. The soft iron core concentrates and guides this magnetic flux.
The changing magnetic flux gets linked with the secondary coil. According to Faraday's law of electromagnetic induction, this induces an alternating e.m.f. (\(V_s\)) across the secondary coil.
The magnitude of the induced e.m.f. in each coil is proportional to the number of turns in that coil. For an ideal transformer (assuming no flux leakage): \[ \frac{V_s}{V_p} = \frac{N_s}{N_p} \] Since for a step-up transformer \(N_s>N_p\), it follows that \(V_s>V_p\). Thus, the output voltage is increased. In an ideal transformer, to conserve power (\(P_{in} = P_{out}\)), the current is stepped down (\(I_s<I_p\)).
Step 3: Circuit Diagram: