On what principle does a transformer operate?

A transformer operates primarily on the principle of mutual induction. This principle describes how two coils of wire can transfer energy through a magnetic field that is created by the alternating current flowing through the primary coil. When current flows through the primary coil, it generates a magnetic field, which then induces a voltage in the secondary coil due to the changing magnetic flux.

This process relies on the characteristics of alternating current (AC), which allows the magnetic field to change direction and strength, facilitating the transfer of energy from one coil to another. Mutual induction is essential for the transformer to step up (increase) or step down (decrease) voltage levels, enabling efficient power distribution in electrical systems.

The other principles listed, like direct current and Ohm's Law, do not apply to how transformers function. Direct current refers to a constant flow of electrical charge, which does not induce a changing magnetic field necessary for transformer operation. Ohm's Law defines the relationship between voltage, current, and resistance in direct current circuits but does not pertain to the operation of transformers. Thus, mutual induction is fundamental to the working of transformers, making it the correct choice.