What is the primary role of the secondary coil in a transformer?

The primary role of the secondary coil in a transformer is to modify voltage levels. In a transformer, there are two coils: the primary and the secondary. The primary coil receives the input voltage and creates a magnetic field, which then induces a voltage in the secondary coil due to electromagnetic induction. The purpose of this process is to either step up (increase) or step down (decrease) the voltage based on the turns ratio between the primary and secondary coils.

When the turns ratio of the secondary to the primary is greater than one, the transformer increases voltage (step-up transformer), and when it is less than one, the transformer decreases voltage (step-down transformer). This ability to change the voltage levels is crucial for efficient power transmission and distribution in electrical systems, as it allows for varying voltage requirements across different applications.

The other choices are related but do not capture the primary function of the secondary coil. Generating magnetic fields is the role of the primary coil, providing an AC supply is a function of the power source rather than the transformer itself, and measuring resistance is completely unrelated to the operation of a transformer.