31.4: Inductors

An inductor, also known as a choke, is a circuit component created to have a specific inductance. Inductors are among the crucial circuit components used in modern electronics, along with resistors and capacitors. They serve as a barrier against changes in a circuit's current. An inductor tends to suppress current changes in an alternating-current circuit that are faster than desired. In a direct-current circuit, an inductor aids in preserving a constant current despite changes in the applied emf.

Although the electric field associated with the magnetic induction effect is non-conservative, there is a real potential difference between the inductor's terminals, caused by conservative electrostatic forces.

One common application of inductance is to allow traffic signals to sense when vehicles are waiting at a street intersection. An electrical circuit with an inductor is placed in the road underneath the location where a waiting car will stop. The car's body increases the inductance, and the circuit changes, sending a signal to the traffic lights to change colors. Similarly, metal detectors used for airport security employ the same technique. A coil or inductor in the metal detector frame acts as a transmitter and a receiver. The pulsed signal from the transmitter coil induces a signal in the receiver. Any metal object in the path affects the circuit's self-inductance. Metal detectors can be adjusted for sensitivity and can also sense the presence of metal on a person.

Inductors are also crucial in fluorescent light fixtures. In such fixtures, the gas that fills the tube is ionized and glows due to the current flowing from the wiring into the gas. The higher the current, the more strongly ionized the plasma and the lower its resistance. If a sufficiently high voltage is given to the plasma, the circuitry outside the fluorescent tube can be damaged. To prevent this, an inductor or magnetic ballast is connected in series with the fluorescent bulb, which keeps the current from exceeding its limits.

An inductor is a two-terminal circuit element consisting of coils of wire. Because of the current flowing in the circuit, magnetic flux passes through the inductor.

When there is a change in the current passing through the inductor, according to Faraday's law, a back emf is generated. This field is the magnetically induced non-conservative electric field.

Since the non-conservative field is nonzero only within the inductor, its integral around the whole loop can be replaced by its integral from one terminal to the other.

Hence, free electrons are accumulated on one of the inductor's terminals to produce a nonzero conservative electric field.

The total electric field is the sum of these two electric fields. If the inductor has negligible resistance, a test charge experiences no force inside. Hence, the total electric field within the coils must be zero. Thus, the non-conservative electric field in this integral can be replaced by the negative of the conservative electric field.

This integral is the potential difference between the terminals of the inductor, which is given by this formula.