A transformer is an essential device used to modify the voltage in an alternating current (AC) circuit.

Transformers operate in AC circuits to alter the voltage of the electrical supply. They consist of two wire coils, known as the primary coil and the secondary coil, which are wound around a magnetic core. When an AC voltage is applied to the primary coil, it generates a magnetic field that induces a voltage in the secondary coil. The transformation of voltage depends on the ratio of the number of turns in the primary coil, denoted as $N_p$, to the number of turns in the secondary coil, denoted as $N_s$. This relationship can be expressed as:

where $V_s$ is the secondary voltage and $V_p$ is the primary voltage.

Transformers serve a variety of functions in AC circuits. They are commonly used to step up (increase) or step down (decrease) the voltage of the electrical supply, which is crucial for the efficient transmission of electrical power over long distances. Additionally, transformers are employed in power supplies to ensure a stable output voltage, and in electronic circuits to provide isolation between different components.

One of the key advantages of transformers is their high efficiency, which results in minimal energy loss during the voltage transformation process. They are also highly reliable due to their lack of moving parts, resulting in a long lifespan. However, it is important to note that transformers are designed exclusively for use with AC circuits and cannot function with direct current (DC) circuits.