Otis Singleton
Electrical capacitance is the ability of a capacitor to store energy in the form of an electric charge. It is measured in farads (F), named after the English physicist Michael Faraday. The capacitance value of a capacitor is determined by the ratio of the electric charge on each conductor to the potential difference (voltage) between them. The larger the plates and the smaller their separation, the greater the charge a capacitor can hold. Capacitors are used in electrical circuits to block direct current (DC) while allowing alternating current (AC) to flow.
| Characteristics | Values |
|---|---|
| Definition | The property of an electric conductor or set of conductors that is measured by the amount of separated electric charge that can be stored on it per unit change in electrical potential. |
| Unit | Farad (F) |
| Sub-units | Microfarads (µF), Picofarads (pF) |
| Capacitor | An electrical component that stores energy in the form of an electric charge. |
| Capacitor Composition | Two or more pieces of conducting material separated by an insulating material. |
| Capacitor Charging | The flow of electrons onto the plates is known as the capacitor's charging current. |
| Capacitor Charging Time | The time span when the capacitor holds the maximum amount of charge as per its capacitance with respect to the voltage. |
| Capacitor Discharging Time | The time span when the current flows to the load from one plate to another until all the charges are dissipated from both plates. |
| Capacitor Plates | The bigger the area of the plates, the more charge they can store. |
| Capacitor Plate Distance | The closer the plates are, the greater the attraction of the opposite charges on them. |
| Capacitor Plate Shape | The conductive metal plates of a capacitor can be square, circular, or rectangular, or they can be of a cylindrical or spherical shape. |
| Dielectric | The insulating material between the capacitor plates. It boosts a capacitor's charging capacity. |
| Dielectric Material | Waxed paper, mica, ceramic, plastic, or some form of liquid gel. |
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What You'll Learn
Capacitors and their ability to store energy
Electrical capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. Capacitors are devices that store electrical energy. They consist of two plates of conducting material (usually a thin metal) sandwiched between an insulator made of ceramic, film, glass, or other materials, even air. The insulator is also known as a dielectric, and it boosts a capacitor's charging capacity. The internal plates are wired to two external terminals, which can be plugged into a circuit.
The amount of energy stored by a capacitor depends on the amount of charge stored on its plates, the area of the plates, the spacing between them, the dielectric material in the space, and the applied voltage. The energy stored in a capacitor is electrical potential energy, and it is related to the charge and voltage between the capacitor plates. The formula that describes this relationship is:
> W = QV
Where W is the energy stored on the capacitor, measured in joules, Q is the amount of charge stored on the capacitor, and V is the voltage across the capacitor.
The maximum amount of energy that can be stored on a capacitor depends on the capacitance and the maximum rated voltage of the capacitor. The stored energy can be quickly released from the capacitor due to its low internal resistance. This property is often used in systems that generate large load spikes, such as audio equipment, uninterruptible power supplies, camera flashes, and pulsed loads such as magnetic coils and lasers. Capacitors are also used in medical devices such as defibrillators, as well as in microelectronics, to supply energy when batteries are charged.
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Capacitance value and its measurement
The capacitance value of an object is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. The SI unit of capacitance is the farad (F), named after the English physicist Michael Faraday. A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates.
There are two types of capacitance: self-capacitance and mutual capacitance. Self-capacitance is the ability of an object to store electric charge, measured by the amount of electric charge that must be added to an isolated conductor to raise its electric potential by one unit of measurement. Mutual capacitance is measured between two components, and is important in the operation of the capacitor, an elementary electronic component designed to add capacitance to an electric circuit. The capacitance between two conductors depends on the geometry, the opposing surface area of the conductors, the distance between them, and the permittivity of any dielectric material between them.
The capacitance of a capacitor can be measured using a digital multimeter, which can identify an unknown or unlabeled capacitor and detect open or shorted capacitors. The capacitor must be disconnected from the circuit to measure its capacitance. The rate of rise of the resulting voltage is then measured; the slower the rate of rise, the larger the capacitance.
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The role of electric circuits
Electric circuits are a fundamental part of modern technology, powering everything from small household devices to large industrial machinery. Understanding the role of electric circuits requires grasping the concept of capacitance, which is the ability of a circuit to store and release energy in the form of an electrical charge.
Capacitance is typically associated with a device called a capacitor, which consists of two or more conductive plates separated by an insulating material known as a dielectric. The conductive plates can be made of metal and come in various shapes, including square, circular, and rectangular. The insulating material can be a natural substance like air, or a manufactured one like waxed paper, plastic, or ceramic.
The capacitor's ability to store electrical energy is due to the separation of charges on its plates. When a direct current (DC) voltage is applied across the capacitor, one plate accumulates a positive charge, while the other accumulates an equal but opposite negative charge. This separation of charges creates a potential difference between the plates, which is the basis of capacitance. The amount of charge that can be stored depends on factors such as the area of the plates, the spacing between them, the dielectric material used, and the applied voltage.
In electric circuits, capacitors play a crucial role in blocking direct current (DC) while allowing alternating current (AC) to flow. This property is utilized in various applications, including household electrical devices and power factor correction circuits. The unit of measurement for capacitance is the farad (F), named after physicist Michael Faraday, with common subdivisions being the microfarad (µF) and picofarad (pF).
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The function of a capacitor in AC and DC circuits
Electrical capacitance is the property of an electric conductor that is measured by the amount of separated electric charge that can be stored on it per unit change in electrical potential. Capacitance also implies the associated storage of electrical energy. Capacitors are passive electronic components that store energy in the form of an electrical charge, producing a potential difference (static voltage) across their plates.
The Function of a Capacitor in a DC Circuit
In a direct current (DC) circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and acts as an insulator. The capacitor's electrode plates are separated by an insulator (air or a dielectric), so no DC current can flow unless the insulation breaks down. Once the capacitor reaches its steady-state condition, an electrical current is unable to flow through the capacitor itself and around the circuit.
The Function of a Capacitor in an AC Circuit
In an alternating current (AC) circuit, the flow of the current passes through the capacitor with little or no resistance. This is because capacitors are repeatedly charged and discharged as the current's polarity alternates, allowing AC current to flow through. Capacitors that are connected to a sinusoidal supply produce reactance from the effects of supply frequency and capacitor size. Capacitance in AC circuits results in a time-dependent current that is shifted in phase by 90 degrees with respect to the supply voltage, producing an effect known as capacitive reactance.
Capacitors are used in a variety of ways in electronic circuits. They are often used to block DC current while passing AC current, which is useful for noise suppression. When a capacitor is connected in parallel and a resistor in series, higher-frequency AC components flow into the ground, creating a low-pass filter (LPF). Conversely, when a capacitor is connected in series and a resistor in parallel, DC components are blocked while higher-frequency AC components are passed through the circuit, creating a high-pass filter (HPF).
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The discovery of capacitance
In 1746, Musschenbroek and his student Andreas Cunaeus at Leyden University succeeded in replicating the experiment with water. Musschenbroek then informed the wider French scientific community of the experiment. It is considered that von Kleist and Musschenbroek independently discovered it. Abbé Nollet, a French experimenter, gave the jar its name, Leyden jar, and sold it as a special type of flask to scientifically curious, wealthy men.
In 1747, a simple but fundamental step in the evolution of the capacitor was taken by the English astronomer John Bevis. Bevis replaced the water in the Leyden jar with metal foil forming a lining on the inside surface of the glass and another covering the outside surface. This form of the capacitor had two conductors of extended area kept nearly equally separated by a thin insulating or dielectric layer. These features have been retained in every modern form of capacitor. A capacitor, also called a condenser, is thus essentially a sandwich of two plates of conducting material separated by an insulating material, or dielectric.
In the 1830s, English natural philosopher Michael Faraday conducted experiments that determined that the material in between the capacitor's plates affected the quantity of charge on the capacitor's plates. Faraday discovered that a charge stored in a capacitor is directly proportional to its capacitance and the applied voltage. The term "capacitor" didn't come into use until the 1920s. For a long time, they were referred to as condensers and they are still called this in some applications and countries. The unit of electric charge is the coulomb and the unit of potential difference is the volt, so the unit of capacitance is one coulomb per volt, or the farad (F), named after Faraday.
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Frequently asked questions
Electrical capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge.
Electrical capacitance is measured in farads (F), named after the English physicist Michael Faraday.
The formula for electrical capacitance is C = q/V, where C is the capacitance, q is the amount of charge, and V is the potential difference.
Self-capacitance refers to the capacitance of an isolated conductor, while mutual capacitance refers to the capacitance between two adjacent conductors, such as the plates of a capacitor.
