The transformer coils of the primary and secondary share NO electrical connection, but current flows through them due to?

In a transformer, the primary and secondary coils are designed to transfer energy through a magnetic field rather than direct electrical connection. This process relies on the principle of mutual induction.

When alternating current flows through the primary coil, it creates a changing magnetic field around it. This changing magnetic field extends to the secondary coil, which is located in proximity to the primary coil but does not have any direct electrical connection. As the magnetic field fluctuates, it induces an electromotive force (EMF) in the secondary coil, which enables current to flow if the circuit is closed.

This phenomenon of inducing current through a magnetic field is what allows transformers to operate efficiently, stepping voltage up or down depending on the number of turns in each coil. Therefore, mutual induction is the correct concept that explains how electrical energy is transferred between two coils without direct electrical connections, making it the correct answer.