Magnetism: Transformers

A transformer is a device that can change the voltage of an alternating current (AC). It consists of two coils of wire, with each coil wrapped around the same iron core. The primary coil is connected to an input voltage, and the secondary coil provides the output voltage.
The operation of a transformer relies on the principle of electromagnetic induction; this means an alternating current in the primary coil will create a changing magnetic field in the iron core, which then induces an alternating current in the secondary coil.
If there are more turns on the primary coil than the secondary, it is a step-down transformer. This decreases the voltage from the primary to the secondary coil.
Conversely, if there are more turns on the secondary coil than the primary, this is a step-up transformer, which increases the voltage from the primary to the secondary coil.
The primary and secondary voltages are related to the number of turns on the primary and secondary coils by the equation: Vp/Vs = Np/Ns. Here, Vp is the primary voltage, Vs is the secondary voltage, Np is the number of turns on the primary coil, and Ns is the number of turns on the secondary coil.
Transformers are not 100% efficient. This lack of efficiency is mostly due to two factors: energy lost as heat due to resistance in the wire (resistive losses), and energy lost because the iron core is magnetically ‘leaky’ (magnetic flux leakage).
To make transformers more efficient, the iron core is often laminated. This reduces energy waste as heat in the core. Also, transformers are often cooled with oil to further reduce heat loss.
Transformers are widely used in the national grid to step up the voltage for transmission and then step it down for domestic use. This is because the higher the voltage, the more efficiently electricity can be transmitted over long distances, as less energy is lost as heat due to resistance in the wires.