インダクタ

An inductor is a two-terminal circuit element consisting of coils of wire that generates a back emf when current changes. According to Faraday's law, magnetic flux through the inductor creates a magnetically induced electric field. This non-conservative field causes charge accumulation on the inductor's terminals, producing a potential difference that opposes current changes in the circuit.

Inductors serve as a barrier against current changes by generating a back emf that opposes variations in current flow. In alternating-current circuits, inductors suppress faster-than-desired current changes. In direct-current circuits, inductors preserve constant current despite changes in applied emf, making them essential for stabilizing circuit behavior.

Although the magnetic induction effect produces a non-conservative electric field, a real potential difference exists between the inductor's terminals due to conservative electrostatic forces. The total electric field within the inductor is the sum of the non-conservative magnetic field and the conservative electrostatic field, resulting in measurable terminal voltage.

Traffic signals use inductors placed in the road beneath waiting vehicles to sense car presence. When a car stops over the inductor, its metal body increases the circuit's inductance, triggering a change that signals the traffic lights to change colors. This application demonstrates inductors' practical role in modern infrastructure and vehicle detection technology.

Metal detectors employ a coil or inductor in the frame that acts as both transmitter and receiver. A pulsed signal from the transmitter coil induces a signal in the receiver. Any metal object in the path affects the circuit's self-inductance, allowing the detector to sense metallic items and adjust sensitivity for airport security applications.

Fluorescent tubes require high voltage to ionize gas, which can damage external circuitry if current becomes excessive. An inductor or magnetic ballast connected in series with the fluorescent bulb limits current flow, protecting the circuit. This prevents damage while maintaining proper ionization and glow intensity in the plasma.

If an inductor has negligible resistance, a test charge experiences no net force inside the coils, requiring the total electric field to be zero. The non-conservative magnetic field is balanced by an equal and opposite conservative electrostatic field, ensuring the integral of the total field around the loop equals the potential difference between terminals.