What is an inductor?
An inductor is a passive electrical component that opposes sudden changes in current even if the voltage across it changes suddenly. Unlike resistors where the current changes instantaneously with voltage, inductors take time to build the current. Inductors are also known as coils or chokes. The fundamental relationship between current and voltage of an inductor is :
$$v=-L\cfrac{di}{dt}$$
Construction of an inductor
An inductor typically consists of a coil of wire wound around a core, which is often made of materials with high magnetic permeability, such as iron. The coil’s inductance is determined by factors like the number of turns in the wire, the coil’s geometry, and the core material.
Circuit symbol of an inductor
In circuit diagrams, inductors are represented using symbols that resemble coiled wires. The symbol typically includes the label “L” to represent inductance.
What is inductance?
Inductance (L) is the property of an inductor that quantifies its ability to store energy in a magnetic field. It is measured in henrys (H). The inductance is directly proportional to the number of turns in the coil and the cross-sectional area enclosed by the coil.
Inductive reactance
Impedance due to resistor and inductor combination
In a circuit containing both resistors and inductors, the overall opposition to the flow of AC current is known as impedance (Z). Impedance includes both resistance (R) and inductive reactance (XL), and it’s given by the formula :
$$Z=\sqrt{R^2+X_L^2}$$
Time constant due to inductance
Inductors resist changes in current, so when a voltage is suddenly applied or removed from an inductor, the current doesn’t change instantaneously. The time it takes for the current to reach about 63.2% of its final value (when charging) or drop to about 36.8% of its initial value (when discharging) is called the time constant (τ) and is given by τ = L/R, where R is the resistance in the circuit.
What is the Self Resonant Frequency of an inductor?
Real inductors have turn-to-turn winding capacitance that acts as if it were a parallel circuit element. Impedance magnitude increases with frequency up to the self-resonant frequency (SRF), where the impedance of an inductor is at its maximum value. At frequencies above the SRF, impedance decreases with increasing frequency because capacitive behavior dominates.
Applications
Inductors slow down current surges or spikes by temporarily storing energy in an electromagnetic field and then releasing it back into the circuit. Some applications are:
- Filtering: They are used in combination with capacitors to create low-pass, high-pass, band-pass, or band-stop filters.
- Energy Storage: Inductors can store energy in magnetic fields and release it when the current changes.
- Transformers: They are a key component in electrical transformers, which transfer energy between circuits through electromagnetic induction.
- Solenoids and motors: Devices such as motors and solenoids use inductors to convert electrical energy into mechanical motion.