# Capacitor

views updated Jun 27 2018

# Capacitor

A capacitor is a device that stores energy in the form of electrical charges. A battery, in contrast, stores energy in the form of chemical potential energy. A capacitor is charged (given some amount of energy to store) by placing a voltage across its two terminals. When the capacitor is partly or fully charged, it can be removed from the circuit. To release the energy stored, the two contacts of the capacitor are connected through some electrical circuit (closed path).

Physically, capacitor consists of two electrical conductors that are not in contact. The conductors are usually separated by a layer of insulating material, a dielectric. The dielectric is not essentialthe conductors could be separated by vacuum, insteadbut in practice it keeps the conductors from touching and increases the amount of charge the capacitor can store. When the capacitor is charged, one conductor becomes positively charged and the other negatively charged. The conductors are not in contact, so a current cannot flow through the capacitor (unless the voltage is raised high enough to break down the device). In this state, the capacitor is storing electrical energy. The energy is released when current flows in the opposite direction, discharging the capacitor and partly or entirely equalizing the voltage difference between its two conductors.

Capacitors take many shapes. The simplest is a parallel-plate capacitor, which consists of two flat conductors (such as metal plates) placed parallel to each other. Larger plates can store more charge, hence more energy. Putting the plates close together also allows the capacitor to store more energy.

The capacitance of a capacitor is the charge on the conductor at any given time divided by the voltage between its conductors. Capacitance expresses the ability of a capacitor to store energy. The capacitance of a parallel-plate capacitor is proportional to the area of the plates divided by the distance between them. This number must then be multiplied by the permittivity of the insulator between the plates. (This is a property of the material and is expressed as a number with appropriate units.) If the permittivity is greater than 1, the dielectric increases the capacitance.

Capacitors come in a wide range of sizes. Banks of large capacitors can store and rapidly release large bursts of electrical energy. Engineers can use such devices for many purposesfor example, testing a systems performance when struck by a bolt of lightning. A camera flash works by retrieving energy from a chemical battery, storing it up in a capacitor, and then releasing it suddenly through a gas-filled tube to cause a bright flash of light. (The capacitor is used because small batteries cannot supply such large, brief currents.) Electronic circuits use large numbers of small capacitors. For example, a typical RAM (random access memory) chip uses millions or billions of microscopic capacitors coupled with switching transistors.

# Capacitor

views updated May 18 2018

# Capacitor

A capacitor stores electrical energy . It is charged by hooking into an electrical circuit. When the capacitor is fully charged a switch is opened and the electrical energy is stored until it is needed. When the energy is needed, the switch is closed and a burst of electrical energy is released.

A capacitor consists of two electrical conductors that are not in contact. The conductors are usually separated by a layer of insulating material, dielectric. The dielectric is not essential but it keeps the conductors from touching. When the capacitor is hooked into an electric circuit with a current, one conductor becomes positively charged and the other negative . The conductors are not in contact, so the current cannot flow across the capacitor. The capacitor is now charged up and the switch can be opened. The capacitor is storing electrical energy. When the energy is needed the capacitor is connected to the circuit needing the energy. The current flows rapidly in the opposite direction, discharging the capacitor in a burst of electrical energy.

Capacitors take many shapes, but the simplest is a parallel plate capacitor. It consists of two flat conductors placed parallel to each other. Larger plates can store more charge and hence more energy. Putting the plates close together also allows the capacitor to store more energy. The capacitance of a capacitor is the charge on the conductor divided by the voltage and is used to measure the ability of a capacitor to store energy. The capacitance of a parallel plate capacitor is proportional to the area of the plates divided by the distance between them. This number must then be multiplied by a constant which is a property of the dielectric between the plates. The dielectric has the effect of increasing the capacitance.

Capacitors come in a wide range of sizes. Banks of large capacitors can store and rapidly release large bursts of electrical energy. Among other uses, engineers can use such devices to test a circuit's performance when struck by a bolt of lightning . On an intermediate scale, a camera flash works by storing energy in a capacitor and then releasing it to cause a quick bright flash of light . Electronic circuits use large numbers of small capacitors. For example, a RAM (Random Access Memory) chip uses hundreds of thousands of very small capacitors coupled with switching transistors in a computer memory. Computer information is stored in a binary code of ones and zeros. A charged capacitor is a one, and an uncharged is a zero . These are just a few example of the many uses of capacitors.

# capacitor

views updated Jun 08 2018

capacitor (condenser) Electrical circuit component that stores charge. It has at least two metal plates and is used principally in alternating current (AC) circuits. The various types include parallel-plate condensers and electrolytic capacitors, the latter having a thin layer of oxide on one electrode. See also electric current

# capacitor

views updated May 23 2018

ca·pac·i·tor / kəˈpasitər/ • n. a device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator.

# capacitor

Updated Aug 13 2018 Print Topic