What do we call coils that transfer energy without any physical or electrical connection?

Inductive coupling refers to the process by which electrical energy is transferred between coils through a magnetic field, without any physical or electrical connection. This principle relies on electromagnetic induction, where a changing magnetic field produced by one coil induces a voltage in another nearby coil. This method is widely used in applications such as wireless charging and transformers. The efficiency of inductive coupling depends on factors such as the distance between the coils, their orientation, and the frequency of the alternating current.

Resistive coupling pertains to the direct transfer of electrical energy through conductive materials, which involves a physical connection. Capacitive coupling involves the transfer of energy through electric fields between capacitors and is often used in circuits where isolation is needed but typically still requires some proximity.

Direct coupling is the straightforward transfer of electrical signals or power through a direct physical connection, such as wires or terminals. This does not involve the principles of electromagnetic or electric field interactions used in inductive or capacitive coupling. Thus, inductive coupling stands out as the correct answer as it uniquely captures the essence of non-physical energy transfer through magnetic fields.