AQA GCSE Physics Paper 2 Practice Exam 2025 - Free AQA GCSE Physics Practice Questions and Study Guide

In a step-down transformer, the primary function is to decrease the voltage from the primary coil to the secondary coil while simultaneously increasing the current. This is based on the principle of energy conservation, where the power input to the transformer must equal the power output, minus any losses.

When the voltage is decreased in a step-down transformer, the current must increase to maintain the power balance. Power is calculated as the product of voltage (V) and current (I), expressed as \( P = V \times I \). Thus, if the voltage decreases, the current must increase proportionally in order to keep the power output consistent with the input.

This explains why the energy conversion in a step-down transformer results in a decrease in voltage and an increase in current. This relationship is fundamental to the operation of transformers and is utilized in various applications, such as reducing high transmission voltages for safer domestic use of electricity.