Capacitor and Capacitance

A capacitor is a passive electronic component that stores electrical energy in an electric field. It is made of two conductors separated by a dielectric. The conductors can be plates, foils, or other shapes. The dielectric is a non-conductive material that separates the conductors.


The capacitance of a capacitor is the ability of the capacitor to store electrical charge. It is measured in farads (F). One farad is equal to one coulomb of charge per volt.

The capacitance of a capacitor is calculated using the following formula:

C = εA/d


  • C is the capacitance (in farads)

  • ε is the permittivity of the dielectric material (in farads per meter)

  • A is the area of each conductor (in square meters)

  • d is the distance between the conductors (in meters)


Also, because capacitors store the energy of the electrons in the form of an electrical charge on the plates the larger the plates and/or smaller their separation the greater will be the charge that the capacitor holds for any given voltage across its plates. In other words, larger plates, smaller distance, more capacitance. By applying a voltage to a capacitor and measuring the charge on the plates, the ratio of the charge Q to the voltage V will give the capacitance value of the capacitor and is therefore given as:

C = Q/V

this equation can also be re-arranged to give the more familiar formula for the

quantity of charge on the plates as:

Q C x V

Although we have said that the charge is stored on the plates of a capacitor, it is more correct to say that the energy within the charge is stored in an "electrostatic field" between the two plates. When an electric current flows into the capacitor, charging it up, the electrostatic field becomes more stronger as it stores more energy. Likewise, as the current flows out of the capacitor, discharging it, the potential difference between the two plates decreases and the electrostatic field decreases as the energy moves out of the plates. The property of a capacitor to store charge on its plates in the form of an electrostatic field is called the Capacitance of the capacitor. Not only that, but capacitance is also the property of a capacitor which resists the change of voltage across it.

Applications of capacitors

Capacitors are used in a wide variety of applications, including:

  • Filtering electrical noise

  • Storing electrical energy

  • Coupling and decoupling circuits

  • Tuning radios and other devices

  • Timing circuits

Capacitors are essential components in many electronic devices, such as computers, televisions, and radios.

Formulas related to capacitors

Here are some other formulas related to capacitors:

  • Energy stored in a capacitor:

E = 1/2CV^2


  • E is the energy stored in the capacitor (in joules)

  • C is the capacitance of the capacitor (in farads)

  • V is the voltage across the capacitor (in volts)

  • Time constant of a capacitor-resistor circuit:

τ = RC


  • τ is the time constant (in seconds)

  • R is the resistance of the resistor (in ohms)

  • C is the capacitance of the capacitor (in farads)

The time constant of a capacitor-resistor circuit is the time it takes for the voltage across the capacitor to charge to 63.2% of its final value when the circuit is connected to a voltage source.


Capacitors are essential components in many electronic devices. They are used to store electrical energy, filter noise, and couple and decouple circuits. Capacitors are available in a variety of types and values, making them suitable for a wide range of applications.