Electricity and Magnetism - Transformers

A transformer is a device used to increase or decrease the $V_{out}$ (output voltage) of an alternating current ($AC$). It consists of a primary coil, a secondary coil, and a soft iron core.

The core is made of soft iron because it is easily magnetized and demagnetized, which helps to concentrate the magnetic field lines and improve flux linkage.

Transformers work on the principle of mutual induction: an $AC$ in the primary coil creates a changing magnetic field, which induces a varying $EMF$ (voltage) in the secondary coil.

A Step-up transformer increases voltage ($V_s > V_p$) and has more turns on the secondary coil ($N_s > N_p$).

A Step-down transformer decreases voltage ($V_s < V_p$) and has fewer turns on the secondary coil ($N_s < N_p$).

In an ideal transformer, there is $100\%$ efficiency, meaning the input power equals the output power: $P_{in} = P_{out}$.

For long-distance power transmission, step-up transformers are used to increase voltage. Since $P = VI$, increasing voltage decreases the current $I$. This reduces power loss in the cables, which is calculated as $P_{loss} = I^2 R$.