What is the fundamental principle that allows a transformer to operate?

• A. Direct current
• B. Self-induction
• C. High resistance
• D. Mutual induction

Answer: (D)

The fundamental principle that allows a transformer to operate is mutual induction. This principle involves two coils, known as the primary and secondary windings, that are placed close to each other. When alternating current flows through the primary winding, it generates a magnetic field that surrounds the winding. This changing magnetic field induces an electromotive force (EMF) in the secondary winding due to the mutual coupling between the two coils. As a result, energy is transferred from the primary coil to the secondary coil without direct electrical connection, thus allowing the transformer to convert voltages efficiently based on the turns ratio of the coils.

Understanding mutual induction is crucial in the context of transformer design and operation because it highlights the reliance on alternating current (AC) to generate the magnetic fields necessary for energy transfer. Direct current, on the other hand, does not create a changing magnetic field and would not facilitate this process.