A transformer is a device that changes an alternating voltage from one value to another. It operates on the principle of mutual electromagnetic induction.

Components

• Primary Coil: The coil to which the input alternating voltage is applied.
• Secondary Coil: The coil across which the output alternating voltage is induced.
• Soft Iron Core: A core that links the two coils. It concentrates and guides the changing magnetic field produced by the primary coil through the secondary coil.

How it Works

1. An alternating voltage applied to the primary coil drives an alternating current through it.
2. This current produces a continuously changing magnetic flux in the soft iron core.
3. The soft iron core guides this changing magnetic flux to link with the secondary coil.
4. According to Faraday's Law of Induction, the changing magnetic flux induces an alternating electromotive force (e.m.f.) across the secondary coil.

For an ideal transformer (assuming 100% efficiency and no energy losses), the following relationships hold:

Voltage and Turns Ratio

The ratio of the secondary voltage ($V_s$) to the primary voltage ($V_p$) is equal to the ratio of the number of turns in the secondary coil ($N_s$) to the number of turns in the primary coil ($N_p$).

Power Conservation

For an ideal transformer, the input power equals the output power.

This implies that the current is inversely proportional to the voltage:

Transformers are essential for the efficient long-distance transmission of electrical power.

1. At the power station, a step-up transformer increases the voltage to a very high value (e.g., 400 kV).
2. This significantly reduces the current ($I$) flowing through the transmission lines.
3. Power loss in the cables, which is given by the formula $P_{loss} = I^2R$, is minimized due to the low current.
4. Near towns and industries, a step-down transformer reduces the voltage to a safer, usable level (e.g., 240V) for consumers.