Question

The secondary windings of a transformer in which the voltage is stepped down are usually made of thicker wire than the primary. Explain why.

Answer 1

A transformer consists of three basic parts. These are an iron core which provides a circuit of low reluctance for magnetic lines of force, a primary winding which receives the electrical energy from the source of applied voltage, and a secondary winding which receives electrical energy by induction from the primary coil. The primary and secondary of this closed core transformer are wound on a closed core to obtain maximum inductive effect between the two coils.
On a step-down transformer there are more turns on the primary coil than the secondary coil. The induced voltage across the primary coil is greater than the applied voltage across the secondary coil or in other words the voltage has been stepped-down".
When a transformer is in operation, there are ac currents in primary and secondary coils. The coils have some resistance and the currents cause heating of the coils, causing some energy to be lost. This loss may be reduced by using low resistance wire for the coils. This is the most important for the high current winding (the secondary coil of a step-down transformer). Thick copper wire is used for this winding, because thick wire of low resistivity has a low resistance.