What is the name of a coil of wire that creates a magnetic field when current passes through it?

• A. Capacitor
• B. Resistor
• C. Inductor
• D. Transformer

Answer: (C)

The main idea here is recognizing a coil that generates a magnetic field when current flows through it. When current moves through a tightly wound coil, it creates a magnetic field around the wire, and wrapping the wire into a coil strengthens the field inside and around the coil. This component is called an inductor. Inductors store energy in their magnetic field and resist changes in current, which is described by inductance. In DC circuits, the magnetic field settles, but in AC circuits the field continually changes and the inductor tends to oppose those changes. Energy stored is proportional to the square of the current, E = 1/2 L I^2.

Capacitors store energy in an electric field between plates, not in a magnetic field. Resistors mainly dissipate energy as heat and do not purposefully create a magnetic field. Transformers use coils to transfer energy via magnetic coupling, but the single coil that creates the magnetic field itself is the inductor.