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Capacitors

Capacitors

Capacitors store electrical energy in the form of electric charge.

Physics

Keywords

condenser, voltage, charge, flash, train, armament, insulator, capacity, electric field, electric current, energy, alternating current, amperage, circuit, power source, izolator, direct current, electro, electric, electrode, electron, physics, integrated circuit, technology

Related items

Scenes

Principle of operation

  • power source
  • capacitor - A device that serves to store electrical charge, and therefore electric energy.
  • consumer

Capacitor types

  • supercapacitor - Electric double-layer capacitor: an electrochemical capacitor with much higher capacitance than other capacitors (several thousand times higher). The use of this type of capacitor is becoming more and more common; it is used where a great amount of electric charge has to be delivered or released very rapidly. It is used, for example, to power camera flashes; to store brake energy in cars, or to start the engine in locomotives.
  • electrolytic capacitor - In this type of capacitor, one of the electrodes is a metal sheet. The metal oxide that forms on the surface of the sheet acts as the dielectric, while the other electrode is a liquid or gel electrolyte. Its main areas of use are power supply units and computer motherboards.
  • mica capacitor - In this type of capacitor the dielectric placed between the plates is made of mica.
  • ceramic capacitor - It contains a ceramic dielectric. This type of capacitor is produced in the largest quantity.

Structure

A capacitor is a device in which energy can be accumulated and stored in the form of electric charge.

The simplest capacitor is the parallel-plate capacitor, which consists of two parallel metal plates separated by an insulating material. The metal plates function as electrodes. The insulating material is called the dielectric; its role is to separate the electrodes and increase the capacitance of the capacitor, that is, the amount of electric charge the capacitor can store.

Charging

  • plates - Large-surface metal electrodes.
  • dielectric - An insulating material that separates the plates. It can increase the capacitance of the capacitor, that is, its ability to store electrical charge. A dielectric can be characterized by its relative permittivity: the ratio of the amount of electric charge stored by a capacitor using that dielectric, compared to a similar capacitor that has vacuum as its dielectric.
  • electric field lines - Imaginary lines used to illustrate the structure of the electric fields. The density of these indicates the strength of the electric field.
  • charge (Q)
  • voltage (U)
  • capacity (C)
  • C=Q/U

The capacitor is charged using electric power. During this process, negative charges leave one electrode and migrate to the other electrode.
Because of the charge difference, an electric field is formed between the two electrodes.

The electric field can be characterized by the electric field strength. This is a vector quantity: it refers to both the magnitude and the direction of the force that acts upon a unit positive charge. In this animation, the black arrows indicate the direction of the field strength.

Plate area

  • charge (Q)
  • voltage (U)
  • capacity (C)
  • C=Q/U

The capacitance of a capacitor depends on a number of factors, such as the shape, size, the distance between its plates and the material of the dielectric. Capacitance not only refers to the amount of charge it can store, but also to the voltage necessary to store a certain amount of charge.

Since the voltage between the plates is directly proportional to the amount of charge they store, the quotient of these two is constant. This quotient is the capacitance, that is: C=Q/U.

The capacitance of a capacitor can be increased in a number of ways. One way to it is to increase the area of the plates. Since the capacitance is directly proportional to the surface area of the plates, if the surface area is doubled, the capacitance is also doubled.

Plate separation

  • charge (Q)
  • voltage (U)
  • capacity (C)
  • C=Q/U

Another way to increase the capacitance is by decreasing the distance between the plates (that is, plate separation). This way the voltage decreases but the amount of charge remains the same.

Dielectric

  • charge (Q)
  • voltage (U)
  • capacity (C)
  • C=Q/U

The capacitance is also greatly affected by the choice of dielectric placed between the plates.

A dielectric can be characterized by its relative permittivity: the ratio of the amount of electric charge stored by a capacitor using that dielectric, compared to a similar capacitor that has vacuum as its dielectric. The permittivity of vacuum is 1; that of air can be considered the same. The relative permittivity of polyethylene is 2, that is, using polyethylene as a dielectric allows the capacitor to store twice as more charge as it could store if there was air between the plates. If there is paper between the plates instead of air, the capacitance will be more than triple, since the relative permittivity of paper is 3.3.

Capacitors in use

  • camera flash - Because capacitors can release the energy they store quickly, they are used when a sudden pulse of high electric current is needed in a device, for example, to start a car or a large loudspeaker, or when using a camera flash. Since charging the capacitor takes some time, we need to wait a bit before we can use the camera flash again.
  • mobile phone - Capacitors are also used in phone chargers and computer power supply units during the rectification of alternating current, to smooth the pulsating output of the rectifier. In the receivers of radios and mobile phones, capacitors with variable capacitance are used to tune the oscillating circuit connected to the antenna to the required frequency.
  • computer memory - Capacitors can be found in most electrical devices. Here are some examples. Computer memory modules (RAM) and some memory cards (e.g. SD) are made up of billions of microscopic capacitors. These store information in the form of electric charges.

Capacitors can be found in most electrical devices. Here are some examples.

Computer memory modules (RAM) and some memory cards (e.g. SD) are made up of billions of microscopic capacitors. These store information in the form of charges.

Because capacitors can release the energy they store more quickly than batteries, they are used when a sudden pulse of high electric current is needed in a device, for example, to start a car or a large loudspeaker, or when using a camera flash. Since charging the capacitor takes some time, we need to wait a bit before we can use the camera flash again.

Capacitors are also used in phone chargers and computer power supply units during the rectification of alternating current, to smooth the pulsating output of the rectifier.

In the receivers of radios and mobile phones, capacitors with variable capacitance are used to tune the oscillating circuit connected to the antenna to the required frequency.

Narration

A capacitor is a device in which energy can be accumulated and stored in the form of electric charge.

The simplest capacitor is the parallel-plate capacitor, which consists of two parallel metal plates separated by an insulating material. The metal plates function as electrodes. The insulating material is called the dielectric; its role is to separate the electrodes and increase the capacitance of the capacitor, that is, the amount of electric charge the capacitor can store.

The capacitor can be charged using an external source of electricity. During this process, negative charges leave one electrode and migrate to the other. Because of the charge difference, an electric field, and therefore voltage, forms between the two electrodes.

The voltage between the two plates depends on the work necessary to move a unit of charge from one plate to the other in the electric field.

The capacitance of a capacitor depends on a number of factors, such as the shape, size, the distance between its plates and the material of the dielectric. Capacitance not only refers to the amount of charge it can store, but also to the voltage necessary to store a certain amount of charge.

Since the voltage between the plates is directly proportional to the amount of charge they store, the quotient of these two is constant. This quotient is the capacitance.

The capacitance of a capacitor can be increased in a number of ways. One way to it is to increase the area of the plates. Since the capacitance is directly proportional to the surface area of the plates, if the surface area is doubled, the capacitance is also doubled.

Another way to increase the capacitance is by decreasing the distance between the plates (that is, plate separation). This way the voltage decreases but the amount of charge remains the same.

The capacitance is also greatly affected by the permittivity of the dielectric between the plates.

If the dielectric between the plates is not vacuum but an insulating material, the electric field strength decreases along with the voltage, although the amount of charge does not change. This is because electrostatic induction takes place within the dielectric, which produces voltage. The direction of the voltage in the insulating material is opposite than the voltage between the plates. The use of an insulating material, therefore, results in a decrease of voltage between the plates and thereby a higher capacity.

The permittivity of vacuum is 1; that of air can be considered the same. The relative permittivity of polyethylene is 2, that is, using polyethylene as a dielectric allows the capacitor to store twice as much charge as it could store if there was air between the plates. If there is paper between the plates instead of air, the capacitance will be more than triple, since the relative permittivity of paper is 3.3.

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