What is a capacitor?

The capacitor is an element used to store electrical energy in the electrical field. A capacitor is a form of passive energy.

Uses of capacitor

In day-to-day life, we use Leyden jars to store various cereals or tanks to store water. The capacitor is used to store electrical charge in electrical field. The capacitor consists of two conductors that are insulated from each other. It is a passive element. The S.I. unit of a capacitor is Farad (F). The simple form of capacitance is shown in the figure.

The symbol of capacitor is shown below:

The diagram represents the circuit diagram of the capacitor.
Circuit representation of a capacitor

Concept of passive element

In an electrical circuit, each device is driven by the flow of electric current and change in voltage. Elements either consume the current and voltage or generate current and voltage. Based on generation and consumption, each electrical component is classified as passive elements or active elements.

Electrical components that consume or store electrical energy are termed passive elements. Resistors, inductors, and capacitors are all classified as passive elements. In an electrical circuit, passive components are connected to the active element to get electrical energy supply at each interval of time.

An electrical device that can generate electrical energy is termed an active element. Current source, voltage source, transistors, and rectifiers are all termed as active elements.

Dielectric medium

The dielectric medium is a medium that has very less electrical conductivity which is not equal to zero. Dielectric medium is not a good conductor. The dielectric medium is present in the capacitor to help it increase the charge storage capacity. The most common materials that can serve the function of a dielectric medium are glass, paper, mica, plastic film, and non-conductive material with an oxide layer.

Nowadays, most capacitor contains dielectric spacers to serve the purpose of a dielectric medium. Dielectric spacers help the capacitor maximize the capacitance. The dielectric medium should have high permittivity, high breakdown voltage, and lesser loss in frequency to increase the capacitor's charge storing capacity.

Earlier, non-conducting materials like papers were used as a dielectric medium which offers high voltage performance, but they absorb a high amount of moisture, which is unacceptable.


The effect produced by the capacitor is known as capacitance. The main function of a capacitor is to add total capacitance to an electrical circuit.

Types of capacitors

Various types of capacitors are easily available in the market. Some of the capacitor types are listed below.

  • Ceramic capacitor : Ceramic capacitors are applied in immoderate-frequency circuits which include audio to R.F. They are also used for excessive-frequency compensation in audio circuits. They are also called disc capacitors. Ceramic capacitors are made by coating two or more small porcelain or ceramic discs with silver and then are stacked collectively to make a capacitor. You can increase or decrease the capacitance of ceramic capacitors by changing the thickness of the ceramic disc used.
  • Power film capacitor : Film capacitors are the most common, usually equipped with various capacitors, including a wide range of capacitors; the difference lies in their dielectric properties.
  • Electrolytic capacitor : Electrolytic capacitors are the most widely used capacitors and have a wide range of endurance capabilities. The working voltages of electrolytic capacitors are as much as about 500 V. Electrolytic capacitors are commonly used in DC power supply circuits.
  • Supercapacitors : The capacitors with an electrochemical ability and excessive capacitance values compared to other capacitors are referred to as supercapacitors.
  • Polarized capacitors : Capacitors with specific positive as well as negative polarities are called polarized capacitors. Care has to be taken that they are connected in perfect polarities when used in a circuit.
  • Mica capacitors : The capacitor that uses Mica, just like the dielectric cloth, is called a mica capacitor. Those capacitors are available in two types which are clamped type and silver type.
  • Variable capacitors : These capacitors require a continuous change in the capacitance by making mechanical or electrical changes as required. For example, capacitors of the transmitter, receiver, and transistor radio for tuning.

Working of the capacitor

Take an example of a battery that we use in daily life. The battery consists of two terminals and inside the battery chemical reaction takes place that completes the circuit. When a chemical reaction takes place, one terminal produces electrons, and another terminal absorbs them. Set the capacitor with one of the same terminal voltages and the same voltage range or greater.

The capacitor is similar to a battery. The only potential difference is that the battery produces electrons, whereas the capacitor stores them. If we try to make a capacitor by using two aluminum foils and a piece of aluminum foil paper, it will work but will not store a large amount of charge and voltage. Inside the capacitor, two terminals connect to metallic plates separated by a dielectric medium.

The diagram represents the components inside the capacitor.
Components of a capacitor
CC0 1.0 Universal Public Domain Dedication | https://commons.wikimedia.org | El cap

In an electric circuit, when the capacitor connects to the battery, the following function takes place:

One plate connected to the battery's negative side absorbs the electrons produced by the battery, whereas the other parallel-plate capacitor connected to the positive terminal loses electrons. Once the capacitor gets charged, it attains a certain voltage. We can find a wide range of capacitors of all capacities.

Functions of the capacitor

  • Store electric charge
  • Prevent dangerous failures
  • It has the ability to pass alternating current without passing direct current.


Capacitor always follows Ohm;s law. The equation that represents the function of the capacitor is as follows.


where C represents the capacitance, ε represents permittivity, d represents a distance between two metallic conductors, and A represents the surface area of the parallel-plate capacitor.

The equation shown below represents the capacitance of a capacitor.


Where C represents capacitance, q shows the charge, and V represents the voltage.

Ideal capacitor

A pure reactive device that has zero resistive effect will be termed as an ideal capacitor. An ideal capacitor will have higher stability concerning temperature changes, and it will not be affected by the atmospheric conditions.

What is 1 Farad?

Take an example of a battery we use in our daily life. One AAA battery can hold 2.8 amp-hours that means it can generate 2.8 A for 1-hour at 1.5 V. Similarly, a 1 F capacitor can store 1 C of electric charge at 1 V.

Common Mistakes

The student generally gets confused in the difference between the capacitor and the capacitance, a capacitor is an element that stores electric charges, whereas capacitance is the property of a capacitor to store charge.

Context and Applications

This subject matter is tremendous inside the expert exam for each undergraduate and graduate publication, mainly for:

  • Bachelor of Technology in the Electrical and Electronics department
  • Bachelor of Science in Physics
  • Master of Science in Physics

The capacitor can be used in various ways in every sector of today's world. Some of the applications are listed below:

  • Radio tuning circuit
  • Timer circuits like a clock, alarm, and counter
  • X-Ray and MRI machines
  • Hybrid cars
  • Lasers
  • Used to eliminate electric ripples
  • Used in electric circuits to block DC voltages.
  • Active and passive elements
  • Capacitance
  • Breakdown voltage
  • The basic function of batteries

Practice problems

Q1.Two metallic conductors present in the capacitor are separated by _____.

  1. Conductors
  2. Insulators
  3. Semiconductors
  4. None of these

Correct option: (b)

Explanation: As discussed above, the capacitor contains two metallic plates separated by a dielectric medium that serve the function of insulators.

Q2. Capacitor obeys ______ law.

  1. Ohms law
  2. KVL
  3. KCL
  4. Coulombs

Correct option: (a)

Explanation: Capacitor always obeys Ohm's law.

Q3. Capacitor is used to store________

  1. Power
  2. Charges
  3. Current
  4. None of these

Correct option- (b)

Explanation- Capacitor is used to store charges in an electric circuit.

Q4. The ultra-capacitors are also called___________

  1. Supercapacitors
  2. Double-layer capacitors
  3. Both of these
  4. None of these

Correct option- (a)

Explanation: The Ultra-capacitors are also called supercapacitors.

Q5. The disadvantage of ultra-capacitors ___________

  1. High Cost
  2. High self-discharge
  3. Both are correct
  4. None of these

Correct option- (c)

Explanation- The main disadvantage of ultracapacitor is high self-discharge and high-cost value.

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