What is the main function of a transformer?

The primary function of a transformer is to change the voltage level of an alternating current (AC) signal. Transformers operate on the principle of electromagnetic induction, and they can either step up (increase) or step down (decrease) voltage levels while maintaining the power level (assuming negligible losses). This capability is essential for efficient power transmission and distribution because higher voltages allow for lower currents, which minimizes energy losses in conductors over long distances.

For example, in power distribution systems, transformers are used to convert high transmission voltages to lower voltages suitable for use in homes and businesses. This transformation not only facilitates safe usage of electricity at the end-user level but also ensures that the power can be delivered efficiently over long distances without excessive losses.

The other options, while related to electrical principles, do not accurately describe the function of a transformer. Converting direct current to alternating current, amplifying signals, or filtering noise involves different types of equipment and mechanisms, such as inverters, amplifiers, and filters, respectively. Each of these devices serves its unique purpose in the broader field of electrical engineering, but they do not fulfill the fundamental role of voltage transformation that a transformer does.