Question

Write the principle of working of a transformer. With the help of a labelled diagram, explain the working of a step-up transformer.

Hint:

In a step-up transformer, the voltage is increased while the current is decreased, according to the law of conservation of energy. The power is ideally the same in both coils (neglecting losses), but the voltage and current are inversely proportional to the number of turns in the primary and secondary coils.

Answer 1

The principle of working of a transformer is based on electromagnetic induction. It works on the principle of Faraday’s Law of Induction and Lenz's Law, which states that when a time-varying magnetic flux is linked with a coil, an electromotive force (emf) is induced in the coil. In a transformer: - AC voltage is applied to the primary coil, creating a varying magnetic flux in the core. - This varying magnetic flux induces an emf (voltage) in the secondary coil, which is proportional to the number of turns in the secondary coil relative to the primary coil. The transformer can either step-up or step-down the voltage depending on the ratio of turns in the primary and secondary coils.

Working of a Step-Up Transformer: In a step-up transformer, the number of turns in the secondary coil is greater than the number of turns in the primary coil. This causes the voltage across the secondary coil to be greater than that across the primary coil. The working process of a step-up transformer is as follows: 1. Primary Coil: An alternating current (AC) is passed through the primary coil. This current creates a time-varying magnetic field in the transformer’s core. 2. Magnetic Field: The time-varying magnetic flux produced by the primary coil induces an emf in the secondary coil. 3. Induced Voltage: Since the number of turns in the secondary coil is more than in the primary, the induced emf in the secondary coil will be higher than the emf in the primary coil. This results in an increase in the voltage in the secondary coil, which is why it is called a step-up transformer. 4. Energy Conservation: The energy supplied to the primary coil is ideally transferred to the secondary coil. However, the current in the secondary coil is reduced in proportion to the increase in voltage, so the power remains the same (neglecting losses). % Labelled Diagram (Diagram should be inserted here)
Mathematical Relation: The relationship between the primary voltage (\(V_p\)), secondary voltage (\(V_s\)), primary number of turns (\(N_p\)), and secondary number of turns (\(N_s\)) is given by the transformer equation: \[ \frac{V_s}{V_p} = \frac{N_s}{N_p} \] For a step-up transformer, \( N_s>N_p \), so \( V_s>V_p \).