The capacitor is an electrical component that stores energy in the form of electric charge and capacitance is the property of material that stores energy. The capacitor is a two-terminal device that has two conducting plates or electrodes separated by some distance.
What is a Capacitor?
A capacitor is a passive circuit element used in various electronic circuits to store electrical energy in the form of electrostatic charge.
A simple capacitor consists of two metal plates placed parallel to each other and has a dielectric medium between them. Two metallic conductors are attached to the metal plates to form the terminals of the capacitor.
A capacitor stores electrical energy during its charging and releases the stored electrical energy while discharging.
The capacitors can be manufactured in various shapes and sizes depending on the applications.
Symbol of Capacitor
The circuit symbol of a capacitor is represented as two parallel line segments representing the metal plates of the capacitor. The following figure shows circuit symbols of non-polarized capacitors, polarized capacitors, and variable capacitors respectively
Types of Capacitors
There are various different types of capacitors available based on polarity, construction, dielectric, etc. Some commonly used types of capacitors are described below:
- Ceramic Capacitor – A ceramic capacitor is a type of capacitor in which ceramic is used as the dielectric medium to store electrostatic charge. It is used in various electronic circuits, due to its low cost and small size.
- Electrolytic Capacitor – An electrolytic capacitor is one in which an electrolyte is used as the dielectric material. It is a polarized capacitor having fixed positive and negative terminal polarity. It is widely used in power supplies, amplifiers, and other electronic circuits where high capacitance is desired.
- Film Capacitor – A capacitor in which a thin plastic film is used as a dielectric medium is called a film capacitor. This type of capacitor is mainly used in DC coupling circuits, timing circuits, noise filters, etc.
- Mica Capacitor – A capacitor that has mica as the dielectric medium is referred to as a mica capacitor. This type of capacitor is primarily used in high-frequency applications.
- Fixed Capacitor – A type of capacitor whose capacitance remains constant is known as a fixed capacitor. It is mainly used in small electronic circuits.
- Variable Capacitor – A variable capacitor is one whose capacitance value can be adjusted as per needs. It is widely used in tuning circuits, antennas, etc.
Read More: Different Types of Capacitors & their Applications
What is the Capacitance of a Capacitor?
Capacitance is a property of a material due to which it can store electrical energy in the form of an electrostatic field. In other words, capacitance is the measure of electrical energy that a material can store. It is denoted by C.
Mathematically, the capacitance of a capacitor is defined as the charge per unit voltage, i.e.
Where Q is the charge on each plate of a capacitor and V is the voltage applied across the capacitor.
Unit of Capacitance
From equation (1), we have,
Hence, the unit of capacitance is coulomb per volt.
But,
Here, Farad (F) is the SI unit of capacitance. It is named in honor of the physicist Michael Faraday.
Farad is a larger unit of capacitance. In practice, several smaller units are used to specify the capacitance of a capacitor. Some commonly used units of capacitance are as follows:
- Microfarad (µF): 1 µF = 10-6 F
- Nanofarad (nF): 1 nF = 10-9 F
- Picofarad (pF): 1 pF = 10-12 F
Formula of Capacitance
To derive the formula of capacitance, consider a simple parallel plate capacitor shown in the following figure.
The capacitance of a capacitor depends upon its physical dimensions. The capacitance C of a capacitor,
- Is directly proportional to area (A) of the cross-section of plates.
- Is inversely proportional to separation (d) between the plates.
- Depends upon the nature of the dielectric material used between the plates.
Therefore, the capacitance of a capacitor is given by,
Or
Where, ε0 is the permittivity of the air, whose value is equal to 8.85 × 10-12 F/m.
If a dielectric material of relative permittivity εr is inserted between the plates of the capacitor, then,
Hence, if a dielectric material of high permittivity is placed between the plates of the capacitor, it will increase the capacitance of the capacitor.
Read More: Formula Derivation of Capacitance
Factors Affecting Capacitance of Capacitor
The capacitance depends on the following factors.
- Surface Area: The capacitance of two plate capacitance is proportional to the surface area(A). The higher the surface area, the higher the capacitance.
- Dielectric Medium: The space between the plates is filled with dielectric material. The permittivity of the dielectric material affects the capacitance. The capacitance is proportional to the permittivity of the dielectric material. The higher the permittivity, the higher the capacitance.
- Distance: The capacitance is inversely proportional to the distance between the plates. Capacitance can be increased by reducing the distance between the plates.
Capacitance and Energy of Capacitor
The energy stored in a capacitor depends on the applied voltage and the capacitance of the capacitor. The formula of energy stored in the capacitor is given below.
Read More: Formula Derivation of Energy stored in a Capacitor
Capacitance of Series Connected Capacitors
The total capacitance of the series-connected capacitor is;
Read More: Derivation of Formula for Capacitor in Parallel
Capacitance of Parallel Connected Capacitors
The total capacitance of the parallel connected capacitor is;
Applications of Capacitor
Capacitors are used to store electrical energy in the form of electrostatic charge. Some common applications of capacitors are listed below:
- Electronic power supplies
- Noise filters
- Signal coupling and decoupling
- Energy storage
- Suppression of voltage spikes
- Signal conditioning and filtering
- Power factor improvement
- Phase split in induction motors
- Store digital information in modern memory devices.
Conclusion
In conclusion, a capacitor is a passive circuit element used in electronic circuits to store electrical energy in the electrostatic field. This property of storing electrical energy is termed capacitance. In this article, we have explained all the important concepts of capacitors and capacitance.
