# Difference between Capacitor and Inductor

Electric TractionPower SystemsUtilisation of Electrical Power

In this article, we will compare and contrast the features of a capacitor and highlight how it differs from an inductor, considering various parameters such as stored energy, flow of current, behaviour in AC and DC circuits, types and applications, etc.

## What is a Capacitor?

An electric circuit element which has ability to store the charge in electrostatic field is known as capacitor. The capacitor is a passive circuit element because it cannot generate and amplify the power in a circuit. Generally, a capacitor consists of two metallic plates, placed parallel to each other and are separated by a dielectric medium. The potential energy is stored in the electric field established between the plates of the capacitor.

The circuit symbol of the capacitor is shown in Figure-1.

The ability of the capacitor of storing electric potential energy in the form of electrostatic field is termed as capacitance of the capacitor. The capacitance of a capacitor is calculated by the following formula and measure in Farad

$$\mathit{C\mathrm{\: =\: }\frac{\epsilon _{\mathrm{0}}\, \epsilon_{r}A}{d}}$$

Where, 𝜖0 and 𝜖𝑟 are the permittivity of air and relative permittivity of dielectric medium respectively. '𝑨' is the cross-section area of each plate and '𝒅' is the distance between the plates.

## What is an Inductor?

An electric circuit element which has ability to store energy in the form of magnetic field is known as inductor. A coil of wire forms a simple inductor. It also a passive element. The circuit symbol of the inductor is shown in Figure-2.

The ability to store energy in the magnetic field is termed as inductance, measured in Henry and given by expression,

$$\mathit{L\mathrm{\: =\: }\frac{N^{\mathrm{2}}\mu A}{l}}$$

Where, 𝑵 is the number of turns in coil, μ is the permeability of core, 𝑨 is the area of core, and 𝒍 is the average length of magnetic core.

## Differences between Capacitor and Inductor

The following table shows the key differences between a capacitor and an inductor.

FactorCapacitorInductor
DefinitionThe circuit element which stores energy in the form of electrostatic field is known as capacitor.A circuit element which has ability to store energy in the form of magnetic field is termed as inductor.
Ability to store energyThe ability by virtue of which capacitor stores energy is known as capacitance.The ability of energy storing is known as inductance.
Relation between voltage and current (in AC circuit)In capacitor, the current leads the voltage across the capacitor by 90°.In case of inductor, the current lags the voltage across the inductor by 90°.
Current flowElectric current does not flow between the plates of a capacitor.Current can flow through the turn of the inductor coil.
Unit of measurementCapacitance of a capacitor is measured in Farad.Inductance is measured in Henry.
Resist to changeThe voltage across a capacitor cannot change abruptly, i.e., the capacitor opposes the change in voltage across it.The current through the inductor cannot change abruptly, i.e. the inductor opposes the change in current through it.
Short circuitCapacitor acts as a short circuit for alternating current.Inductor acts as a short circuit for direct current.
Condition of steady stateIn steady state condition (or in DC circuit), the capacitor acts as an open circuit.In steady state, the inductor acts as a short circuit.
Combination in seriesWhen capacitors are connected in series, then equivalent capacitance is determined by,$$\mathrm{\frac{1}{\mathit{C_{eq}}}\mathrm{\: =\: }\frac{1}{\mathit{C_{\mathrm{1}}}}\mathrm{\: +\: }\frac{1}{\mathit{C_{\mathrm{2}}}}\mathrm{\: +\: }\frac{1}{\mathit{C_{\mathrm{3}}}}\mathrm{\: +\: }\cdot \cdot \cdot }$$
When inductors are joined in series combination, the effective inductance is given by,$$\mathrm{\mathit{L_{eq}\mathrm{\: =\: }L_{\mathrm{1}}\mathrm{\: +\: }L_{\mathrm{2}}\mathrm{\: +\: }L_{\mathrm{3}}\mathrm{\: +\: }\cdot \cdot \cdot }}$$
Combination in ParallelWhen capacitors are connected in parallel, their equivalent capacitance is$$\mathrm{\mathit{C_{eq}\mathrm{\: =\: }C_{\mathrm{1}}\mathrm{\: +\: }C_{\mathrm{2}}\mathrm{\: +\: }C_{\mathrm{3}}\mathrm{\: +\: }\cdot \cdot \cdot }}$$
When inductors are connected in parallel, then equivalent inductance is$$\mathrm{\frac{1}{\mathit{L_{eq}}}\mathrm{\: =\: }\frac{1}{\mathit{L_{\mathrm{1}}}}\mathrm{\: +\: }\frac{1}{\mathit{L_{\mathrm{2}}}}\mathrm{\: +\: }\frac{1}{\mathit{L_{\mathrm{3}}}}\mathrm{\: +\: }\cdot \cdot \cdot }$$
TypesTypes of capacitors are defined based on the dielectric material used in the capacitor.There are various types of inductors available. Some of them are coupled inductor, ceramic core inductor, moulded inductor, multi-layer inductor, etc.
Energy storedThe energy stored by the capacitor is given by$$\mathrm{\mathit{E\mathrm{\: =\: }\mathrm{\frac{1}{2}} CV^{\mathrm{2}}}}$$
The energy stored by the inductor is given by,$$\mathrm{\mathit{E\mathrm{\: =\: }\mathrm{\frac{1}{2}} LI^{\mathrm{2}}}}$$
ApplicationsCapacitors are used for energy storage, power conditioning, power factor correction, suppression and coupling, motor starting, oscillators, etc.Inductors are used in motors, generators, filters and choke, relays, transformers sensors, etc.

## Conclusion

From the above discussion, we can conclude that both inductors and capacitors are passive circuit elements that store energy in the magnetic field and electrostatic field, respectively. Both of these elements are extensively used in electrical and electronic circuit designing. Hence, the knowledge of capacitors and inductors can help an individual select either of them according to the requirements of a circuit.

Updated on 20-May-2022 13:21:54