A capacitor is a passive electronic component that stores electrical energy in an electric field. It consists of two conductors separated by a non-conductive material called a dielectric. When a voltage is applied across the conductors, electric charges of equal magnitude but opposite polarity build up on each surface. This results in an internal electric field. Capacitance is a measure of the amount of charge stored on each conductor for a given voltage. It depends on the surface area of the conductors, their separation distance, and the dielectric material between them. Capacitors are used widely in electronic circuits for blocking DC while allowing AC to pass, in power supplies, tuned circuits in radios, power transmission systems, and other applications.
A capacitor is a device that stores electrons and is made up of two conductors separated by an insulator. Capacitors come in various sizes, shapes, and can be customized. They are used to store electric charge and in circuits to block DC signals while passing AC signals. There are several types of capacitors including non-polarized, polarized, variable, and trimmer capacitors which differ in how they can be connected and whether their capacitance can be adjusted. Capacitors have many uses including in timing circuits, filters, and charge pump circuits.
A capacitor is a device that stores electrons and is made up of two conductors separated by an insulator. Capacitors come in different sizes, shapes, and models and can store varying amounts of charge depending on their design. There are several types of capacitors including non-polarized capacitors that can be connected either way in a circuit, polarized capacitors that must be connected correctly, variable capacitors whose capacitance can be adjusted, and trimmer capacitors designed to be set during circuit assembly.
This document discusses capacitors and their uses. It begins by describing the basic construction of a capacitor, which consists of two conducting plates separated by an insulating material called a dielectric. It then discusses different types of capacitors like electrolytic, ceramic, silver mica, and polyester capacitors. The document also covers various applications of capacitors such as for energy storage, pulsed power, power factor correction, capacitive coupling, in tank circuits, and as components in electronic filters. In conclusion, the document provides a brief overview of the key aspects of capacitors.
This presentation introduces capacitors and their mechanism. It explains that a basic capacitor contains two parallel plates separated by an insulating material, and that it stores electrical charge between the plates. The unit of capacitance is the Farad. Common types of capacitors include mica, ceramic, plastic film, and electrolytic capacitors, which are polarized. Variable capacitors can adjust capacitance and are used in devices like radios. Modern technology uses semiconductor variable capacitors called varactors.
A capacitor is a device that stores electric charge between two conductors separated by an insulator. There are different types of capacitors including non-polarized capacitors that can be connected either way in a circuit, polarized capacitors that must be connected with the correct polarity, variable capacitors whose capacitance can be varied by moving plates, and trimmer capacitors designed to be adjusted once and then left without further adjustment. Capacitors are used in timing circuits, as filters to block DC signals, and in radio tuners.
Capacitors are energy storage devices composed of two conductive plates separated by an insulator. The capacitance of a capacitor depends on the plate area, distance between plates, and dielectric material. An ideal capacitor acts as an open circuit at steady state but the voltage must be continuous. The equivalent capacitance for capacitors in parallel is the sum of the individual capacitances, while for capacitors in series it is the inverse of the sum of the reciprocals of the individual capacitances.
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Resistors are very useful components in healthcare electronics so every healthcare engineers to learn about all these kinds of basic components
A capacitor is a device that stores electric charge between two conductive plates separated by an insulator. When a voltage is applied across the plates, charges of opposite polarity accumulate on each plate. The amount of charge stored depends on the capacitor's capacitance, which is determined by the size, number, and distance between plates as well as the dielectric material between the plates. Capacitors are used in electrical circuits for functions like energy storage, voltage regulation, timing, and filtering. They can be connected in parallel to increase total capacitance or in series to decrease it. Common applications include power supplies, audio equipment, and sensors.
A capacitor is a device that stores electrons and is made up of two conductors separated by an insulator. Capacitors come in various sizes, shapes, and can be customized. They are used to store electric charge and in circuits to block DC signals while passing AC signals. There are several types of capacitors including non-polarized, polarized, variable, and trimmer capacitors which differ in how they can be connected and whether their capacitance can be adjusted. Capacitors have many uses including in timing circuits, filters, and charge pump circuits.
A capacitor is a device that stores electrons and is made up of two conductors separated by an insulator. Capacitors come in different sizes, shapes, and models and can store varying amounts of charge depending on their design. There are several types of capacitors including non-polarized capacitors that can be connected either way in a circuit, polarized capacitors that must be connected correctly, variable capacitors whose capacitance can be adjusted, and trimmer capacitors designed to be set during circuit assembly.
This document discusses capacitors and their uses. It begins by describing the basic construction of a capacitor, which consists of two conducting plates separated by an insulating material called a dielectric. It then discusses different types of capacitors like electrolytic, ceramic, silver mica, and polyester capacitors. The document also covers various applications of capacitors such as for energy storage, pulsed power, power factor correction, capacitive coupling, in tank circuits, and as components in electronic filters. In conclusion, the document provides a brief overview of the key aspects of capacitors.
This presentation introduces capacitors and their mechanism. It explains that a basic capacitor contains two parallel plates separated by an insulating material, and that it stores electrical charge between the plates. The unit of capacitance is the Farad. Common types of capacitors include mica, ceramic, plastic film, and electrolytic capacitors, which are polarized. Variable capacitors can adjust capacitance and are used in devices like radios. Modern technology uses semiconductor variable capacitors called varactors.
A capacitor is a device that stores electric charge between two conductors separated by an insulator. There are different types of capacitors including non-polarized capacitors that can be connected either way in a circuit, polarized capacitors that must be connected with the correct polarity, variable capacitors whose capacitance can be varied by moving plates, and trimmer capacitors designed to be adjusted once and then left without further adjustment. Capacitors are used in timing circuits, as filters to block DC signals, and in radio tuners.
Capacitors are energy storage devices composed of two conductive plates separated by an insulator. The capacitance of a capacitor depends on the plate area, distance between plates, and dielectric material. An ideal capacitor acts as an open circuit at steady state but the voltage must be continuous. The equivalent capacitance for capacitors in parallel is the sum of the individual capacitances, while for capacitors in series it is the inverse of the sum of the reciprocals of the individual capacitances.
The full basics of electronics can be look over in our link http://bit.ly/2PPv0mv
Resistors are very useful components in healthcare electronics so every healthcare engineers to learn about all these kinds of basic components
A capacitor is a device that stores electric charge between two conductive plates separated by an insulator. When a voltage is applied across the plates, charges of opposite polarity accumulate on each plate. The amount of charge stored depends on the capacitor's capacitance, which is determined by the size, number, and distance between plates as well as the dielectric material between the plates. Capacitors are used in electrical circuits for functions like energy storage, voltage regulation, timing, and filtering. They can be connected in parallel to increase total capacitance or in series to decrease it. Common applications include power supplies, audio equipment, and sensors.
Ceramic capacitors are the most commonly used type of capacitor. They consist of alternating layers of ceramic and metal electrodes. Multilayer ceramic capacitors (MLCCs) allow for large capacitance values in small packages. Ceramic capacitors are used for coupling, decoupling, filtering, and smoothing circuits. They have advantages like being non-polarized and able to withstand high voltages. However, ceramic capacitors generally have lower maximum capacitance values than other types and can be subject to microphonic effects.
Capacitors and resistors have several applications in electronics circuits. Capacitors can smooth power supply voltage into direct current, eliminate power spikes by placing a small capacitor across logic circuits, and pass alternating signals while blocking direct current. Resistor-capacitor circuits can integrate or filter input signals and differentiate waves.
This is small Power point presentation about different types of capacitors. It deals with different applications of different capacitors.This ppt has some important classification of different capacitors
The document discusses different types of capacitors and their applications including energy storage, smoothing, filtering, and coupling. It also covers capacitor calculations, testing, and component identification. The document then discusses inductors and their applications in filtering and other circuits. It covers transformers, switches, relays, contactors, circuit breakers, fuses, breadboards, semiconductors, and PN junctions. Finally, it discusses different types of diodes and their applications in rectification and clipping circuits.
Our group members for this project are A. F. M. Foysal Islam, Pias Ahmmed, Md. Abed Ceum, Md. Farhan Islam, and Pronay Kumar Tarafdaer. A capacitor is a passive two-terminal electrical component that stores energy in its electric field by accumulating positive charge on one plate and negative charge on the other when connected to a battery. Increasing the surface area of the plates, decreasing the spacing between plates, and increasing the dielectric constant of the material between the plates improves a capacitor's ability to store charge. There are fixed, electrolytic, and variable types of capacitors that use different materials and configurations.
This document summarizes different types of capacitors. It discusses ceramic capacitors, film capacitors, electrolytic capacitors, supercapacitors, variable capacitors, and trimming capacitors. Ceramic capacitors use ceramic material as the dielectric and come in different classes with varying accuracy and stability. Film capacitors use plastic film as the dielectric and come in metal foil or metallized film varieties. Electrolytic capacitors have a high capacitance-voltage product and use an oxide layer as the dielectric. Variable and trimming capacitors allow changing the capacitance through mechanical adjustment. Supercapacitors bridge the gap between electrolytic capacitors and batteries with lower voltage but higher capacity.
Composed of two conductive plates separated by an insulator (or dielectric).
Commonly illustrated as two parallel metal plates separated by a distance, d.
C = e A/d
where e = er eo
er is the relative dielectric constant
eo is the vacuum permittivity
A capacitor stores electric charge by having two conductors separated by an insulator. The amount of charge stored is proportional to the potential difference between the conductors. Capacitance is a measure of how much charge can be stored at a given potential difference. Parallel plate capacitors have capacitance that depends on the area of the plates and their separation distance. Dielectrics between the plates increase capacitance.
A capacitor is an electronic component that stores an electrical charge. It consists of two conducting surfaces separated by an insulating material. The amount of charge a capacitor can store is defined by its capacitance, which depends on the size and separation of the conducting plates and the material between them. When a voltage is applied across a capacitor's plates, electric current initially flows high as the capacitor charges, then tapers off to zero as it reaches full charge. This exponential charging and discharging process is characterized by the capacitor's time constant, the product of its capacitance and the resistance in the charging/discharging circuit.
The document discusses different types of electrical components including resistors, capacitors, and inductors. It provides details on:
- Resistors including types (fixed, variable), connection methods (series, parallel), and color coding.
- Capacitors including what they are, units of measurement, connection methods, charging/discharging behavior, types, and practical construction.
- Inductors including definition, magnetism principles, types (fixed, variable, ferromagnetic core, air core, toroidal core, laminated core, powdered iron core), and applications.
Diodes are two-terminal semiconductor devices that allow current to flow in only one direction. There are several types of diodes used for different applications. Some of the main types are light emitting diodes (LEDs) which produce light when forward biased, zener diodes which provide a stable reference voltage, and rectifier diodes which are used to rectify alternating current in power supplies. Other types include Schottky diodes, photodiodes, varactor diodes, and avalanche diodes. Diodes are widely used in electronics for applications such as power regulation, signal detection, light emission, and voltage regulation.
The document discusses different types of capacitors including fixed capacitors such as paper, mica and ceramic capacitors, as well as electrolytic and variable capacitors. It provides details on the construction and characteristics of each type of capacitor, as well as their common applications in electronic circuits. Fixed capacitors have a set capacitance value, while variable capacitors allow the capacitance to be adjusted by changing the position of movable plates.
This document provides an overview of capacitors including: what a capacitor is, how it is measured, how to connect capacitors in series and parallel circuits, and how to make a simple capacitor. It discusses that a capacitor consists of two plates separated by an insulator and stores electrical energy. The document outlines that it will cover the capacitor unit, reasons for its use, connection configurations, equivalent circuits, formulas, examples, charging and discharging curves, and materials needed to make a basic capacitor. Contact information is provided for any questions.
There are several types of capacitors including non-polarized, polarized, variable, and trimmer capacitors. Non-polarized capacitors can be connected either way in a circuit and include ceramic, mica, and some electrolytic capacitors. Polarized capacitors maintain a positive and negative terminal and are often used in timing circuits or to filter signals. Variable capacitors have movable plates that allow the capacitance to be varied, making them useful in radio tuners. Trimmer capacitors are small variable capacitors adjusted with a screwdriver during circuit assembly.
The document provides an introduction to electronic passive components. It discusses resistors, capacitors, inductors, and transformers. Resistors are electronic components that oppose the flow of current and come in fixed and variable types. Capacitors are components that store electric charge and also come in fixed and variable types. Inductors are coils of wire that oppose changes in current flow. Transformers are made of two coils of wire wound on a core and transfer energy from one circuit to another through mutual induction. The document provides details on various types of these components, their construction, properties, and applications.
Capacitors are two-terminal electrical components that store equal and opposite charges on conductors separated by an insulating dielectric. They were first invented in 1745 by Ewald von Kleist who discovered that charge could be stored by connecting a high-voltage generator to a glass jar filled with water. Daniel Gralath later combined multiple jars in parallel to increase storage capacity. Benjamin Franklin concluded that the charge was stored on the glass rather than in the water. Early capacitors included Leyden jars which were the main technology until 1900, though they were not as flexible as modern capacitors. The term 'condenser' was first used by Alessandro Volta in 1782 to describe devices that could store higher densities of electric
This document defines and explains capacitance and capacitors. It discusses that capacitance is the ability of a system to store electric charge, and is measured in Farads. A capacitor is made of two conductive plates separated by a dielectric material. The capacitance of a capacitor depends on the plate area, distance between plates, and dielectric material. Capacitors are used to temporarily store electric energy and have various applications in electronics.
A capacitor is an electronic component that stores electric charge between two conductors separated by an insulator. Capacitors are used in applications like computer memory, camera flashes, and surge protectors. The amount of charge a capacitor can store is proportional to the potential difference between its plates and is known as its capacitance, measured in Farads. Common types of capacitors include parallel-plate and cylindrical capacitors.
With this mantra success is sure to come your way. At APEX INSTITUTE we strive our best to realize the Alchemist's dream of turning 'base metal' into 'gold'.
Ceramic capacitors are the most commonly used type of capacitor. They consist of alternating layers of ceramic and metal electrodes. Multilayer ceramic capacitors (MLCCs) allow for large capacitance values in small packages. Ceramic capacitors are used for coupling, decoupling, filtering, and smoothing circuits. They have advantages like being non-polarized and able to withstand high voltages. However, ceramic capacitors generally have lower maximum capacitance values than other types and can be subject to microphonic effects.
Capacitors and resistors have several applications in electronics circuits. Capacitors can smooth power supply voltage into direct current, eliminate power spikes by placing a small capacitor across logic circuits, and pass alternating signals while blocking direct current. Resistor-capacitor circuits can integrate or filter input signals and differentiate waves.
This is small Power point presentation about different types of capacitors. It deals with different applications of different capacitors.This ppt has some important classification of different capacitors
The document discusses different types of capacitors and their applications including energy storage, smoothing, filtering, and coupling. It also covers capacitor calculations, testing, and component identification. The document then discusses inductors and their applications in filtering and other circuits. It covers transformers, switches, relays, contactors, circuit breakers, fuses, breadboards, semiconductors, and PN junctions. Finally, it discusses different types of diodes and their applications in rectification and clipping circuits.
Our group members for this project are A. F. M. Foysal Islam, Pias Ahmmed, Md. Abed Ceum, Md. Farhan Islam, and Pronay Kumar Tarafdaer. A capacitor is a passive two-terminal electrical component that stores energy in its electric field by accumulating positive charge on one plate and negative charge on the other when connected to a battery. Increasing the surface area of the plates, decreasing the spacing between plates, and increasing the dielectric constant of the material between the plates improves a capacitor's ability to store charge. There are fixed, electrolytic, and variable types of capacitors that use different materials and configurations.
This document summarizes different types of capacitors. It discusses ceramic capacitors, film capacitors, electrolytic capacitors, supercapacitors, variable capacitors, and trimming capacitors. Ceramic capacitors use ceramic material as the dielectric and come in different classes with varying accuracy and stability. Film capacitors use plastic film as the dielectric and come in metal foil or metallized film varieties. Electrolytic capacitors have a high capacitance-voltage product and use an oxide layer as the dielectric. Variable and trimming capacitors allow changing the capacitance through mechanical adjustment. Supercapacitors bridge the gap between electrolytic capacitors and batteries with lower voltage but higher capacity.
Composed of two conductive plates separated by an insulator (or dielectric).
Commonly illustrated as two parallel metal plates separated by a distance, d.
C = e A/d
where e = er eo
er is the relative dielectric constant
eo is the vacuum permittivity
A capacitor stores electric charge by having two conductors separated by an insulator. The amount of charge stored is proportional to the potential difference between the conductors. Capacitance is a measure of how much charge can be stored at a given potential difference. Parallel plate capacitors have capacitance that depends on the area of the plates and their separation distance. Dielectrics between the plates increase capacitance.
A capacitor is an electronic component that stores an electrical charge. It consists of two conducting surfaces separated by an insulating material. The amount of charge a capacitor can store is defined by its capacitance, which depends on the size and separation of the conducting plates and the material between them. When a voltage is applied across a capacitor's plates, electric current initially flows high as the capacitor charges, then tapers off to zero as it reaches full charge. This exponential charging and discharging process is characterized by the capacitor's time constant, the product of its capacitance and the resistance in the charging/discharging circuit.
The document discusses different types of electrical components including resistors, capacitors, and inductors. It provides details on:
- Resistors including types (fixed, variable), connection methods (series, parallel), and color coding.
- Capacitors including what they are, units of measurement, connection methods, charging/discharging behavior, types, and practical construction.
- Inductors including definition, magnetism principles, types (fixed, variable, ferromagnetic core, air core, toroidal core, laminated core, powdered iron core), and applications.
Diodes are two-terminal semiconductor devices that allow current to flow in only one direction. There are several types of diodes used for different applications. Some of the main types are light emitting diodes (LEDs) which produce light when forward biased, zener diodes which provide a stable reference voltage, and rectifier diodes which are used to rectify alternating current in power supplies. Other types include Schottky diodes, photodiodes, varactor diodes, and avalanche diodes. Diodes are widely used in electronics for applications such as power regulation, signal detection, light emission, and voltage regulation.
The document discusses different types of capacitors including fixed capacitors such as paper, mica and ceramic capacitors, as well as electrolytic and variable capacitors. It provides details on the construction and characteristics of each type of capacitor, as well as their common applications in electronic circuits. Fixed capacitors have a set capacitance value, while variable capacitors allow the capacitance to be adjusted by changing the position of movable plates.
This document provides an overview of capacitors including: what a capacitor is, how it is measured, how to connect capacitors in series and parallel circuits, and how to make a simple capacitor. It discusses that a capacitor consists of two plates separated by an insulator and stores electrical energy. The document outlines that it will cover the capacitor unit, reasons for its use, connection configurations, equivalent circuits, formulas, examples, charging and discharging curves, and materials needed to make a basic capacitor. Contact information is provided for any questions.
There are several types of capacitors including non-polarized, polarized, variable, and trimmer capacitors. Non-polarized capacitors can be connected either way in a circuit and include ceramic, mica, and some electrolytic capacitors. Polarized capacitors maintain a positive and negative terminal and are often used in timing circuits or to filter signals. Variable capacitors have movable plates that allow the capacitance to be varied, making them useful in radio tuners. Trimmer capacitors are small variable capacitors adjusted with a screwdriver during circuit assembly.
The document provides an introduction to electronic passive components. It discusses resistors, capacitors, inductors, and transformers. Resistors are electronic components that oppose the flow of current and come in fixed and variable types. Capacitors are components that store electric charge and also come in fixed and variable types. Inductors are coils of wire that oppose changes in current flow. Transformers are made of two coils of wire wound on a core and transfer energy from one circuit to another through mutual induction. The document provides details on various types of these components, their construction, properties, and applications.
Capacitors are two-terminal electrical components that store equal and opposite charges on conductors separated by an insulating dielectric. They were first invented in 1745 by Ewald von Kleist who discovered that charge could be stored by connecting a high-voltage generator to a glass jar filled with water. Daniel Gralath later combined multiple jars in parallel to increase storage capacity. Benjamin Franklin concluded that the charge was stored on the glass rather than in the water. Early capacitors included Leyden jars which were the main technology until 1900, though they were not as flexible as modern capacitors. The term 'condenser' was first used by Alessandro Volta in 1782 to describe devices that could store higher densities of electric
This document defines and explains capacitance and capacitors. It discusses that capacitance is the ability of a system to store electric charge, and is measured in Farads. A capacitor is made of two conductive plates separated by a dielectric material. The capacitance of a capacitor depends on the plate area, distance between plates, and dielectric material. Capacitors are used to temporarily store electric energy and have various applications in electronics.
A capacitor is an electronic component that stores electric charge between two conductors separated by an insulator. Capacitors are used in applications like computer memory, camera flashes, and surge protectors. The amount of charge a capacitor can store is proportional to the potential difference between its plates and is known as its capacitance, measured in Farads. Common types of capacitors include parallel-plate and cylindrical capacitors.
With this mantra success is sure to come your way. At APEX INSTITUTE we strive our best to realize the Alchemist's dream of turning 'base metal' into 'gold'.
A short circuit occurs when current passes through a shortened path in the circuit, causing the current to become very large and the wires to heat up. An octopus connection is a fire hazard because it causes the current, voltage, and resistance to become very high. An ammeter is connected in series to measure current, while a voltmeter is connected in parallel. Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.
Voltage, current, resistance, and ohm's lawAnaya Zafar
This document provides an overview of key electrical concepts including voltage, current, resistance, and Ohm's law. It defines voltage as the potential difference between two points, current as the rate of flow of electrical charge, and resistance as a material's opposition to current. It then explains Ohm's law, which quantifies the relationship between voltage, current and resistance in a circuit. The document also includes an example circuit using an LED and resistor to limit current based on Ohm's law calculations.
The document discusses different topics related to inductance including:
1) Self-inductance is defined as the ratio of the total flux linkage to the current through a solenoid or coil.
2) The flux density of a toroid coil is proportional to the current through it and inversely proportional to its radius.
3) Mutual inductance is defined as the ability of one coil to produce an emf in a nearby coil when the current in the first coil changes, and is proportional to the flux from the first coil that is coupled to the second coil.
This document discusses voltage, potential difference, and electromotive force in electric circuits. It defines that in a series circuit, the total voltage is equal to the sum of the voltages across each component. In a parallel circuit, the voltage is the same across each component branch, whereas in a series circuit the current is the same through each component but the voltage splits across them. It provides examples of measuring voltages in series and parallel circuits and explains that the energy transferred per coulomb is equal across the whole circuit due to conservation of energy.
This document describes an experiment to study the discharge process of an RC circuit. The objectives are to measure the current and charge of a capacitor during discharge and determine the time constant of the RC circuit. The experiment involves charging a capacitor using a power supply, then discharging it through a resistor while measuring the voltage over time. Data is plotted and the slope is used to calculate the experimental time constant, which is compared to the theoretical value calculated from the circuit components.
The document discusses the concept of resonance through examples such as bridges and mechanical systems. It explains that resonance occurs when an object vibrates at greater amplitudes due to another source emitting its natural frequency. Specifically, it discusses how the Tacoma Narrows Bridge collapsed in 1940 due to wind-induced oscillations resonating with the structure of the bridge. It also summarizes the collapse of the Nimitz Freeway in 1989, which was caused by an earthquake matching the bridge's resonant frequency. The document provides background on concepts like kinetic energy, potential energy, amplitude, and frequency to explain the physics of resonance.
This document discusses resonance in series and parallel RLC circuits. It defines key parameters for both circuit types including resonance frequency, half-power frequencies, bandwidth, and quality factor. The series resonance circuit is analyzed showing that impedance is purely resistive at resonance, with maximum current and unity power factor. Parallel resonance is also examined, with admittance being purely conductance at resonance. Formulas for calculating important resonant characteristics are provided.
Georg Simon Ohm was a German physicist born in 1789 who discovered Ohm's Law, which states that the current through a conductor is directly proportional to the voltage applied and inversely proportional to the resistance of the conductor. Ohm spent nine years studying electric circuits experimentally and took great care to ensure accuracy in his experiments. In 1827, he was able to show from his experiments the simple mathematical relationship between resistance, current, and voltage that became known as Ohm's Law. Ohm's Law can be expressed as V=IR, where V is voltage, I is current, and R is resistance.
The document reports on an experiment to verify Ohm's Law by measuring the current and voltage in circuits with known resistors. Two resistors were tested (R1 = 11.2Ω, R2 = 21.1Ω). Measurements were taken using a voltmeter, ammeter, and ohmmeter. The data was plotted and linear fits confirmed Ohm's Law. Slopes from the plots matched the resistor values to within measurement error, verifying Ohm's Law.
A capacitor stores electric charge by having two conductors separated by an insulator. Common applications include computer memory, camera flashes, and surge protectors. The amount of charge stored is proportional to the potential difference between the plates. When a dielectric is placed between the plates, it increases the capacitance by a factor called the dielectric constant. Energy is stored in a capacitor as 1/2 CV^2 and is released when the capacitor discharges through a circuit.
Capacitors are electronic components that can store electric charge. They are made of two conductive plates separated by an insulator called a dielectric. The amount of charge a capacitor can store is called its capacitance, which depends on the plate area, distance between plates, and the dielectric material. Capacitors can be connected in series or parallel in circuits. In parallel, the capacitances add up, while in series, they add reciprocally. Charged capacitors store energy that can be calculated using the capacitor's voltage and capacitance. The rate at which capacitors charge and discharge depends on resistance and capacitance through the time constant.
In a series circuit, current has no choice but to follow a single path through components like lamps. A single switch can control all lamps, and adding more lamps reduces brightness. In a parallel circuit, current can split and follow multiple paths, so a switch controls individual lamps and adding lamps does not affect brightness. Series and parallel circuits differ in how switches function and how additional lamps are affected.
Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit. Voltage is the "push" of electricity and is measured in volts. Current is the flow of electricity and is measured in amps. Resistance opposes the flow of current and is measured in ohms. Ohm's Law states that current is directly proportional to voltage and inversely proportional to resistance. Using Ohm's Law, the voltage, current, or resistance in a circuit can be calculated if two of the three values are known. Resistors are used to decrease voltage in a circuit and are marked with color bands to indicate their resistance value. Circuits can be connected in series or parallel, and understanding circuit diagrams
This document is Syed Azeem Ahmed's assignment for the integrated circuits subject. It includes summaries of inductors, capacitors, and resistors. The summaries define each component, describe their construction and operation. Inductors produce voltage proportional to current change. Capacitors store electric charge between conductors separated by dielectric. Resistors limit current in circuits. The document also includes the resistor color code chart.
Resonance occurs when an object is driven at its natural frequency, causing oscillations to build up rapidly. There are three conditions for resonance: 1) an object with a natural frequency, 2) a forcing function at the same frequency, and 3) a lack of damping. When these conditions are met, the oscillations reinforce each other and grow larger. Examples of resonance include playground swings, washing machines, opera singers shattering wine glasses, and bridges collapsing from marching soldiers.
This document discusses circuits, current, potential difference, and problem solving. It begins by defining an electric circuit and its key components. It then explains that in a series circuit, the current at every point is the same and the sum of the potential differences equals the total potential difference across the whole circuit. In a parallel circuit, the current from the source equals the sum of currents in the branches, and the potential differences across branches are the same. Several example problems are given to calculate current, potential difference, resistance, and other circuit properties for series and parallel circuits.
The document discusses Kirchhoff's laws, which are two fundamental laws of circuit analysis:
1) Kirchhoff's voltage law (KVL) states that the sum of the voltages around any closed loop is equal to zero.
2) Kirchhoff's current law (KCL) states that the algebraic sum of the currents entering and leaving any node in a circuit is equal to zero.
The document provides examples of applying KVL and KCL to analyze circuits and solve for unknown voltages and currents. It also includes a quiz on Kirchhoff's laws.
1. The document discusses capacitors, eddy currents, Lenz's law, and Faraday's laws of electromagnetic induction. It provides details on how capacitors work, different types of capacitors, and their uses.
2. It explains that when a conductor moves through a magnetic field, an eddy current is induced in the conductor due to electromagnetic induction. Lenz's law states that the direction of this induced current will oppose the change that created it.
3. Faraday's laws of electromagnetic induction establish that a voltage is induced in a circuit when there is a change in the magnetic flux through the circuit. The magnitude of this induced voltage is proportional to the rate of change of flux.
Capacitors are electrical components that can store electric charge. They consist of two conductors separated by an insulator. The amount of charge a capacitor can store depends on its capacitance, which is determined by the size, number, and distance between the conductors and the dielectric material between them. When voltage is applied across a capacitor's plates, electric charges of equal magnitude but opposite polarity build up on each plate. Capacitors are used widely in electrical circuits to filter signals or store energy. They can be connected in series or parallel configurations, which affects how voltage and charge are distributed across the capacitors.
The document provides an overview of capacitance, magnetism, and electromagnetism for an ASE certification exam. It defines key concepts such as capacitance, dielectric materials, magnetic flux lines, electromagnets, and how electricity and magnetism are related. Objectives include explaining factors that influence capacitance and how capacitors are used in various applications such as filters, memory storage, and microphones.
A supercapacitor or ultra capacitor is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors. They are of particular interest in automotive applications for hybrid vehicles and as supplementary storage for battery electric vehicles.
This document discusses energy storage devices known as capacitors. It describes the basic construction of a capacitor using two conductive plates separated by an insulating material. The capacitance of a capacitor depends on the plate area, distance between plates, and the dielectric material. Several types of capacitors are introduced, including fixed, electrolytic, variable, and electric double layer capacitors. The key electrical properties of capacitors are explained, such as how charge is stored, the relationship between charge, voltage, and capacitance, and equations for charging, discharging, power, and equivalent capacitance.
A capacitor consists of two conductive plates separated by a dielectric material. When a voltage is applied, opposite charges accumulate on each plate. The ability of a capacitor to store charge is known as capacitance. Factors like plate area, distance between plates, and the dielectric material's permittivity determine capacitance. Dielectric materials are used in capacitors to increase capacitance by reducing the electric field between plates. Common dielectric materials include mica, ceramics, and polymers. Ferroelectric and piezoelectric materials can also interconvert electrical and mechanical energy.
This document presents an overview of ultracapacitors by Bharat Gupta for Dr. Anwar Sadat. It begins with an introduction to ultracapacitors, their principles, construction, taxonomy, comparisons to batteries and capacitors, advantages and disadvantages, and applications. The body of the document then provides more detailed explanations of these topics, describing the technological aspects of ultracapacitors including their principles of storing charge, construction with electrodes and electrolytes, different types (electrochemical double-layer, pseudocapacitors, and hybrids), performance comparisons in terms of energy and power densities, and various applications from transportation to military uses. The document concludes that ultracapacitors have great potential in applications requiring high power and cycling
A capacitor consists of two conductive plates separated by an insulating material. When a voltage is applied, opposite charges accumulate on each plate. The ability of a capacitor to store charge is known as capacitance. Capacitance depends on the plate area, distance between plates, and the dielectric material's permittivity. Dielectric materials with higher permittivity increase a capacitor's charge storage ability. Common dielectric materials include mica, ceramics, and polymers. Some materials exhibit piezoelectricity or ferroelectricity based on their polarization response to electric fields.
1) The document discusses capacitors and dielectrics, including how capacitors work, capacitors in series and parallel, and the molecular model of induced charges in dielectrics.
2) Key topics covered include parallel plate capacitors, calculating capacitance, applications of capacitors like in touch screens and defibrillators, and how dielectrics increase the capacitance of capacitors by reducing the potential difference for a given charge.
3) When a dielectric is placed between the plates of a capacitor, the capacitance increases and the potential difference decreases for a given charge, with the ratio of the capacitances with and without the dielectric defined as the dielectric constant.
1) Capacitance refers to an object's ability to store electrical charge. A capacitor consists of conducting plates separated by an insulator and is used to store electrical energy.
2) The capacitance of a parallel plate capacitor depends on the plate area, distance between plates, and the dielectric material between the plates - with larger areas, smaller distances, and higher-permittivity dielectrics increasing capacitance.
3) When a dielectric is placed in a capacitor, it polarizes under the electric field and reduces the overall field strength. This lowers the voltage needed to store a given charge, effectively increasing the capacitor's capacitance.
The document discusses different types of dielectric materials including solid, liquid, and gaseous dielectrics. Solid dielectrics are effective electrical insulators and can transmit or emit light. Liquid dielectrics are used in high voltage applications to prevent electric discharges and provide insulation and cooling. Common examples include transformer oil. Gaseous dielectrics also prevent electric discharges in high voltage equipment and commonly used gases include air, nitrogen, sulfur hexafluoride and perfluorocarbons. Dielectrics are used in capacitors to store charge and increase capacitance. Dielectric resonators are used in oscillator circuits to provide a frequency reference. Transformer oil is used to cool transformers and provide electrical insulation between live parts.
- The document describes a water analogy to explain how a capacitor works, where water pressure and volume correspond to voltage and capacitance.
- It then discusses what a real capacitor is made of - metal plates separated by an insulating material. The closer the plates, or the higher the dielectric constant of the insulator, the greater the capacitance.
- Experiments are described to observe the exponential charging and discharging curves of a capacitor using a circuit with a variable resistor and multimeter. The time constant is defined and its relationship to capacitance and resistance is shown.
1. This document provides an overview of basic electronic components and concepts including voltage, current, power, resistors, capacitors, semiconductors, and diodes. It describes what each component is, how it works, and examples of its applications.
2. Key concepts covered include Ohm's law, series and parallel circuits, alternating current, inductors, transformers, and the use of diodes for rectification and protection from voltage spikes.
3. Semiconductors are described as materials that can be doped to be either electron-rich n-type or hole-rich p-type, and a diode consists of a junction between n-type and p-type materials that only allows current
1) This document provides an overview of basic electronic components and concepts including voltage, current, power, resistors, capacitors, semiconductors, and diodes. It describes what each component is, how it works, and examples of its applications.
2) Key concepts covered include Ohm's law, series and parallel circuits, alternating current, inductors, transformers, and the use of diodes for rectification and protection from reverse polarity.
3) Semiconductors are described as materials that can be doped to become either electron-rich n-type or hole-rich p-type, and a diode consists of a junction between n-type and p-type materials that allows current to
Electrical properties of tissues can be passive or active. Passive properties refer to how tissues behave in an electric field, while active properties refer to electricity generated from tissue activity. Live tissue acts as a special conductor allowing electric currents from both external sources and internal plasma membranes. Current can be direct (DC) or alternating (AC). Tissue impedance depends on properties like cell membrane conductance and resistance that influence how electric currents flow.
1. Resistance is a property that opposes the flow of electric current in a circuit. Ohm's law states that voltage is directly proportional to current.
2. An inductor stores energy in the form of a magnetic field when current flows through it. It impedes changes in current. Inductors are classified based on their core material like iron, air, or ferrite.
3. A capacitor stores electric charge between two conductors separated by an insulator. Capacitance is its ability to store charge. Common capacitor types include parallel plate, spherical, and cylindrical capacitors.
Capacitors store energy and have frequency-dependent behavior. They are made up of two conducting plates separated by an insulator. The voltage across a capacitor is proportional to the charge stored on its plates according to the equation Q = CV, where Q is the charge, C is the capacitance, and V is the voltage. The relationship between current and voltage in a capacitor is ic(t) = C dvc(t)/dt, meaning that current is proportional to the rate of change of voltage. If the voltage across a capacitor is decreasing, the current will be negative.
This is a basic presentation about the Capacotors with iths basic knowledge about some equations also.
It is a little longer but you will get the general information about the capacitors.
It is well divided into 4 portions.
Ultracapacitors store electrical energy electrostatically through polarization of an electrolytic solution at the interface between the electrolyte and electrode, rather than through chemical reactions like batteries. They complement batteries by providing higher power density and longer lifespan than batteries, though lower energy density. Ultracapacitors consist of porous carbon electrodes separated by an electrolyte and membrane, and store energy via ion adsorption at the electrode-electrolyte interface when voltage is applied. They provide rapid charging and discharging compared to batteries.
Electrostatic induction occurs when a charged object places a nearby conductor in an electrostatic field, inducing a charge on the conductor without direct contact. A capacitor is composed of two conductors separated by an insulator and can store electric charge and energy. The capacitance of a parallel plate capacitor increases if a dielectric material is placed between the plates due to the dielectric's higher relative permittivity than air. Capacitors can be combined in series or parallel configurations.
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1. Capacitor
From Wikipedia, the free encyclopedia
This article is about the electronic component. For the physical phenomenon, see capacitance. For an overview of
various kinds of capacitors, see types of capacitor.
Miniature low-voltage capacitors, by a cm ruler
A typical electrolytic capacitor
A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in
an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors
separated by a dielectric (insulator); for example, one common construction consists of metal foils separated by a
thin layer of insulating film. Capacitors are widely used as parts of electrical circuits in many common electrical
devices.
When there is a potential difference (voltage) across the conductors, a static electric field develops across the
dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in
the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads.
This is the ratio of the electric charge on each conductor to the potential difference between them.
The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor
conductors are often called "plates," referring to an early means of construction. In practice, the dielectric between
the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a
breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass,
in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular
frequencies, in electric power transmission systems for stabilizing voltage and power flow, and for many other
purposes.[1]
Contents [hide]
1 History
2 Theory of operation
2.1 Overview
2.2 Hydraulic analogy
2.3 Energy of electric field
2.4 Current-voltage relation
2.5 DC circuits
2.6 AC circuits
2.7 Parallel-plate model
2. 2.8 Networks
3 Non-ideal behaviour
3.1 Breakdown voltage
3.2 Equivalent circuit
3.3 Ripple current
3.4 Capacitance instability
3.5 Current and voltage reversal
3.6 Leakage
3.7 Electrolytic failure from disuse
4 Capacitor types
4.1 Dielectric materials
4.2 Structure
5 Capacitor markings
5.1 Example
6 Applications
6.1 Energy storage
6.2 Pulsed power and weapons
6.3 Power conditioning
6.3.1 Power factor correction
6.4 Supression and coupling
6.4.1 Signal coupling
6.4.2 Decoupling
6.4.3 Noise filters and snubbers
6.5 Motor starters
6.6 Signal processing
6.6.1 Tuned circuits
6.7 Sensing
7 Hazards and safety
8 See also
9 Notes
3. 10 References
11 External links
[edit]History
Battery of four Leyden jars in Museum Boerhaave, Leiden, the Netherlands.
In October 1745, Ewald Georg von Kleist of Pomerania in Germany found that charge could be stored by connecting
a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar.[2] Von Kleist's hand
and the water acted as conductors, and the jar as a dielectric (although details of the mechanism were incorrectly
identified at the time). Von Kleist found, after removing the generator, that touching the wire resulted in a painful
spark. In a letter describing the experiment, he said "I would not take a second shock for the kingdom of France."[3]
The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the
Leyden jar, after the University of Leiden where he worked.[4]
Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage
capacity. Benjamin Franklin investigated the Leyden jar and "proved" that the charge was stored on the glass, not in
the water as others had assumed. He also adopted the term "battery",[5][6] (denoting the increasing of power with
a row of similar units as in a battery of cannon), subsequently applied to clusters of electrochemical cells.[7] Leyden
jars were later made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent
arcing between the foils.[citation needed] The earliest unit of capacitance was the 'jar', equivalent to about 1
nanofarad.[citation needed]
Leyden jars or more powerful devices employing flat glass plates alternating with foil conductors were used
exclusively up until about 1900, when the invention of wireless (radio) created a demand for standard capacitors,
and the steady move to higher frequencies required capacitors with lower inductance. A more compact construction
began to be used of a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or
folded into a small package.
Early capacitors were also known as condensers, a term that is still occasionally used today. The term was first used
for this purpose by Alessandro Volta in 1782, with reference to the device's ability to store a higher density of
electric charge than a normal isolated conductor.[8]
[edit]Theory of operation
Main article: Capacitance
[edit]Overview
Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the field
and increases the capacitance.
4. A simple demonstration of a parallel-plate capacitor
A capacitor consists of two conductors separated by a non-conductive region.[9] The non-conductive region is called
the dielectric. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric media are glass, air,
paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is
assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric
field. The conductors thus hold equal and opposite charges on their facing surfaces,[10] and the dielectric develops
an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes
a voltage of one volt across the device.[11]
The capacitor is a reasonably general model for electric fields within electric circuits. An ideal capacitor is wholly
characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V
between them:[9]
Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case,
capacitance is defined in terms of incremental changes:
[edit]Hydraulic analogy
In the hydraulic analogy, a capacitor is analogous to a rubber membrane sealed inside a pipe. This animation
illustrates a membrane being repeatedly stretched and un-stretched by the flow of water, which is analogous to a
capacitor being repeatedly charged and discharged by the flow of current.
In the hydraulic analogy, current flowing through a wire is analogous to water flowing through a pipe. A capacitor is
like a rubber membrane sealed inside a pipe. Water molecules cannot pass through the membrane, but some water
can move by stretching the membrane. The analogy clarifies a few aspects of capacitors:
The flow of current alters the charge on a capacitor, just as the flow of water changes the position of the membrane.
More specifically, the effect of an electric current is to increase the charge of one plate of the capacitor, and
decrease the charge of the other plate by an equal amount. This is just like how, when water flow moves the rubber
membrane, it increases the amount of water on one side of the membrane, and decreases the amount of water on
the other side.
The more a capacitor is charged, the larger its voltage drop, i.e. the more it "pushes back" against the charging
current. This is analogous to the fact that the more a membrane is stretched, the more it pushes back on the water.
Current can flow "through" a capacitor even though no individual electron can get from one side to the other. This is
analogous to the fact that water can flow through the pipe even though no water molecule can pass through the
rubber membrane. Of course, the flow cannot continue the same direction forever; the capacitor will experience
dielectric breakdown, and analogously the membrane will eventually break.
The capacitance describes how much charge can be stored on a capacitor for a given "push" (voltage drop). A very
stretchy, flexible membrane corresponds to a higher capacitance than a stiff membrane.
A charged-up capacitor is storing potential energy, analogously to a stretched membrane.
5. [edit]Energy of electric field
Work must be done by an external influence to "move" charge between the conductors in a capacitor. When the
external influence is removed the charge separation persists in the electric field and energy is stored to be released
when the charge is allowed to return to its equilibrium position. The work done in establishing the electric field, and
hence the amount of energy stored, is given by:[12]
[edit]Current-voltage relation
The current i(t) through any component in an electric circuit is defined as the rate of flow of a charge q(t) passing
through it, but actual charges, electrons, cannot pass through the dielectric layer of a capacitor, rather an electron
accumulates on the negative plate for each one that leaves the positive plate, resulting in an electron depletion and
consequent positive charge on one electrode that is equal and opposite to the accumulated negative charge on the
other. Thus the charge on the electrodes is equal to the integral of the current as well as proportional to the voltage
as discussed above. As with any antiderivative, a constant of integration is added to represent the initial voltage v
(t0). This is the integral form of the capacitor equation,[13]
Taking the derivative of this, and multiplying by C, yields the derivative form,[14]
The dual of the capacitor is the inductor, which stores energy in a magnetic field rather than an electric field. Its
current-voltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing C
with the inductance L.
[edit]DC circuits
See also: RC circuit
A simple resistor-capacitor circuit demonstrates charging of a capacitor.
A series circuit containing only a resistor, a capacitor, a switch and a constant DC source of voltage V0 is known as a
charging circuit.[15] If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it
follows from Kirchhoff's voltage law that
Taking the derivative and multiplying by C, gives a first-order differential equation,
At t = 0, the voltage across the capacitor is zero and the voltage across the resistor is V0. The initial current is then i
(0) =V0 /R. With this assumption, the differential equation yields
where is the time constant of the system.
6. As the capacitor reaches equilibrium with the source voltage, the voltages across the resistor and the current
through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates
exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero.
[edit]AC circuits
See also: reactance (electronics) and electrical impedance#Deriving the device specific impedances
Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes
between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows
any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies
may be found. The reactance and impedance of a capacitor are respectively
where j is the imaginary unit and ω is the angular frequency of the sinusoidal signal. The - j phase indicates that the
AC voltage V = Z I lags the AC current by 90°: the positive current phase corresponds to increasing voltage as the
capacitor charges; zero current corresponds to instantaneous constant voltage, etc.
Impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency
signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an AC "short circuit" or AC
coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit
in AC analysis—those frequencies have been "filtered out".
Capacitors are different from resistors and inductors in that the impedance is inversely proportional to the defining
characteristic, i.e. capacitance.
[edit]Parallel-plate model
Dielectric is placed between two conducting plates, each of area A and with a separation of d
The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as
air). The model may also be used to make qualitative predictions for other device geometries. The plates are
considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that
the width of the plates is much greater than their separation d, the electric field near the centre of the device will be
uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates
Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation
.
The capacitance is therefore greatest in devices made from materials with a high permittivity, large plate area, and
small distance between plates. However solving for maximum energy storage using Ud as the dielectric strength per
distance and capacitor voltage at the capacitor's breakdown voltage limit V = Vbd = Udd.
7. we see that the maximum energy is a function of dielectric volume, permittivity, and dielectric strength per distance.
So increasing the plate area while decreasing the separation between the plates while maintaining the same volume
has no change on the amount of energy the capacitor can store. Care must be taken when increasing the plate
separation so that the above assumption of the distance between plates being much smaller than the area of the
plates is still valid for these equations to be accurate.
Several capacitors in parallel.
[edit]Networks
See also: Series and parallel circuits
For capacitors in parallel
Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is
apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each
capacitor contributes to the total surface area.
For capacitors in series
Several capacitors in series.
Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up. The
capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total
voltage difference from end to end is apportioned to each capacitor according to the inverse of its capacitance. The
entire series acts as a capacitor smaller than any of its components.
Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage
power supply. The voltage ratings, which are based on plate separation, add up, if capacitance and leakage currents
for each capacitor are identical. In such an application, on occasion series strings are connected in parallel, forming a
matrix. The goal is to maximize the energy storage of the network without overloading any capacitor.
This paragraph needs attention from an expert on the subject. See the talk page for details. WikiProject Electronics
or the Electronics Portal may be able to help recruit an expert. (May 2011)
Series connection is also sometimes used to adapt polarized electrolytic capacitors for bipolar AC use. Two polarized
electrolytic capacitors are connected back to back to form a bipolar capacitor with half the capacitance. The anode
film can only withstand a small reverse voltage however.[16] This arrangement can lead to premature failure as the
anode film is broken down during the reverse-conduction phase and partially rebuilt during the forward phase.[17] A
non-polarized electrolytic capacitor has both plates anodized so that it can withstand rated voltage in both
directions; such capacitors have about half the capacitance per unit volume of polarized capacitors.
8. [edit]Non-ideal behaviour
Capacitors deviate from the ideal capacitor equation in a number of ways. Some of these, such as leakage current
and parasitic effects are linear, or can be assumed to be linear, and can be dealt with by adding virtual components
to the equivalent circuit of the capacitor. The usual methods of network analysis can then be applied. In other cases,
such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot be used,
the effect must be dealt with separately. There is yet another group, which may be linear but invalidate the
assumption in the analysis that capacitance is a constant. Such an example is temperature dependence. Finally,
combined parasitic effects such as inherent inductance, resistance, or dielectric losses can exhibit non-uniform
behavior at variable frequencies of operation.
[edit]Breakdown voltage
Main article: Breakdown voltage
Above a particular electric field, known as the dielectric strength Eds, the dielectric in a capacitor becomes
conductive. The voltage at which this occurs is called the breakdown voltage of the device, and is given by the
product of the dielectric strength and the separation between the conductors,[18]
The maximum energy that can be stored safely in a capacitor is limited by the breakdown voltage. Due to the scaling
of capacitance and breakdown voltage with dielectric thickness, all capacitors made with a particular dielectric have
approximately equal maximum energy density, to the extent that the dielectric dominates their volume.[19]
For air dielectric capacitors the breakdown field strength is of the order 2 to 5 MV/m; for mica the breakdown is 100
to 300 MV/m, for oil 15 to 25 MV/m, and can be much less when other materials are used for the dielectric.[20] The
dielectric is used in very thin layers and so absolute breakdown voltage of capacitors is limited. Typical ratings for
capacitors used for general electronics applications range from a few volts to 1 kV. As the voltage increases, the
dielectric must be thicker, making high-voltage capacitors larger per capacitance than those rated for lower voltages.
The breakdown voltage is critically affected by factors such as the geometry of the capacitor conductive parts; sharp
edges or points increase the electric field strength at that point and can lead to a local breakdown. Once this starts
to happen, the breakdown quickly tracks through the dielectric until it reaches the opposite plate, leaving carbon
behind causing a short circuit.[21]
The usual breakdown route is that the field strength becomes large enough to pull electrons in the dielectric from
their atoms thus causing conduction. Other scenarios are possible, such as impurities in the dielectric, and, if the
dielectric is of a crystalline nature, imperfections in the crystal structure can result in an avalanche breakdown as
seen in semi-conductor devices. Breakdown voltage is also affected by pressure, humidity and temperature.[22]
[edit]Equivalent circuit
Two different circuit models of a real capacitor
An ideal capacitor only stores and releases electrical energy, without dissipating any. In reality, all capacitors have
imperfections within the capacitor's material that create resistance. This is specified as the equivalent series
resistance or ESR of a component. This adds a real component to the impedance:
9. As frequency approaches infinity, the capacitive impedance (or reactance) approaches zero and the ESR becomes
significant. As the reactance becomes negligible, power dissipation approaches PRMS = VRMS² /RESR.
Similarly to ESR, the capacitor's leads add equivalent series inductance or ESL to the component. This is usually
significant only at relatively high frequencies. As inductive reactance is positive and increases with frequency, above
a certain frequency capacitance will be canceled by inductance. High-frequency engineering involves accounting for
the inductance of all connections and components.
If the conductors are separated by a material with a small conductivity rather than a perfect dielectric, then a small
leakage current flows directly between them. The capacitor therefore has a finite parallel resistance,[11] and slowly
discharges over time (time may vary greatly depending on the capacitor material and quality).
[edit]Ripple current
Ripple current is the AC component of an applied source (often a switched-mode power supply) (whose frequency
may be constant or varying). Some types of capacitors, primarily tantalum and aluminium electrolytic capacitors,
usually have a rating for maximum ripple current. Ripple current causes heat to be generated within the capacitor
due to the current flow across the slightly resistive plates in the capacitor. The equivalent series resistance (ESR) is
the amount of external series resistance one would add to a perfect capacitor to model this. ESR does not exactly
equal the actual resistance of the plates.
Tantalum electrolytic capacitors are limited by ripple current and generally have the highest ESR ratings in the
capacitor family. Exceeding their ripple limits tends to result in explosive failure.
Aluminium electrolytic capacitors, the most common type of electrolytic, suffer a large shortening of life expectancy
if rated ripple current is exceeded.
Ceramic capacitors generally have no ripple current limitation and have some of the lowest ESR ratings.
[edit]Capacitance instability
The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by
degradation of the dielectric. The type of dielectric, ambient operating and storage temperatures are the most
significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by
heating the component above the Curie point. Aging is fastest near the beginning of life of the component, and the
device stabilizes over time.[23] Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic
capacitors, this occurs towards the end of life of the component.
Temperature dependence of capacitance is usually expressed in parts per million (ppm) per °C. It can usually be
taken as a broadly linear function but can be noticeably non-linear at the temperature extremes. The temperature
coefficient can be either positive or negative, sometimes even amongst different samples of the same type. In other
words, the spread in the range of temperature coefficients can encompass zero. See the data sheet in the leakage
current section above for an example.
Capacitors, especially ceramic capacitors, and older designs such as paper capacitors, can absorb sound waves
resulting in a microphonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC
current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio
applications, potentially causing feedback or unintended recording. In the reverse microphonic effect, the varying
electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate
audible sound, but drains energy and stresses the dielectric and the electrolyte, if any.
[edit]Current and voltage reversal
10. Current reversal occurs when the flow of current changes direction. Voltage reversal is the change of polarity in a
circuit. Reversal is generally described as the percentage of the maximum rated voltage that reverses polarity. In DC
circuits this will usually be less than 100%, (often in the range of 0 to 90%), whereas AC circuits experience 100%
reversal.
In DC circuits and pulsed circuits, current and voltage reversal are affected by the damping of the system. Voltage
reversal is encountered in RLC circuits that are under-damped. The current and voltage reverse direction, forming a
harmonic oscillator between the inductance and capacitance. The current and voltage will tend to oscillate and may
reverse direction several times, with each peak being lower than the previous, until the system reaches an
equilibrium. This is often referred to as ringing. In comparison, critically damped or over-damped systems usually do
not experience a voltage reversal. Reversal is also encountered in AC circuits, where the peak current will be equal in
each direction.
For maximum life, capacitors usually need to be able to handle the maximum amount of reversal that a system will
experience. An AC circuit will experience 100% voltage reversal, while under-damped DC circuits will experience less
than 100%. Reversal creates excess electric fields in the dielectric, causes excess heating of both the dielectric and
the conductors, and can dramatically shorten the life-expectancy of the capacitor. Reversal ratings will often affect
the design considerations for the capacitor, from the choice of dielectric materials and voltage ratings to the types of
internal connections used.[24]
[edit]Leakage
Leakage is equivalent to a resistor in parallel with the capacitor. Constant exposure to heat can cause dielectric
breakdown and excessive leakage, a problem often seen in older vacuum tube circuits, particularly where oiled
paper and foil capacitors were used. In many vacuum tube circuits, interstage coupling capacitors are used to
conduct a varying signal from the plate of one tube to the grid circuit of the next stage. A leaky capacitor can cause
the grid circuit voltage to be raised from its normal bias setting, causing excessive current or signal distortion in the
downstream tube. In power amplifiers this can cause the plates to glow red, or current limiting resistors to overheat,
even fail. Similar considerations apply to component fabricated solid-state (transistor) amplifiers, but owing to lower
heat production and the use of modern polyester dielectric barriers this once-common problem has become
relatively rare.
[edit]Electrolytic failure from disuse
Electrolytic capacitors are conditioned when manufactured by applying a voltage sufficient to initiate the proper
internal chemical state. This state is maintained by regular use of the equipment. If a system using electrolytic
capacitors is disused for a long period of time it can lose its conditioning, and will generally fail with a short circuit
when next operated, permanently damaging the capacitor. To prevent this in tube equipment, the voltage can be
slowly brought up using a variable transformer (variac) on the mains, over a twenty or thirty minute interval.
Transistor equipment is more problementic as such equipment may be sensitive to low voltage ("brownout")
conditions, with excessive currents due to improper bias in some circuits.
[edit]Capacitor types
Main article: Types of capacitor
Practical capacitors are available commercially in many different forms. The type of internal dielectric, the structure
of the plates and the device packaging all strongly affect the characteristics of the capacitor, and its applications.
Values available range from very low (picofarad range; while arbitrarily low values are in principle possible, stray
(parasitic) capacitance in any circuit is the limiting factor) to about 5 kFsupercapacitors.
11. Above approximately 1 microfarad electrolytic capacitors are usually used because of their small size and low cost
compared with other technologies, unless their relatively poor stability, life and polarised nature make them
unsuitable. Very high capacity supercapacitors use a porous carbon-based electrode material.
[edit]Dielectric materials
Capacitor materials. From left: multilayer ceramic, ceramic disc, multilayer polyester film, tubular ceramic,
polystyrene, metalized polyester film, aluminum electrolytic. Major scale divisions are in centimetres.
Most types of capacitor include a dielectric spacer, which increases their capacitance. These dielectrics are most
often insulators. However, low capacitance devices are available with a vacuum between their plates, which allows
extremely high voltage operation and low losses. Variable capacitors with their plates open to the atmosphere were
commonly used in radio tuning circuits. Later designs use polymer foil dielectric between the moving and stationary
plates, with no significant air space between them.
In order to maximise the charge that a capacitor can hold, the dielectric material needs to have as high a permittivity
as possible, while also having as high a breakdown voltage as possible.
Several solid dielectrics are available, including paper, plastic, glass, mica and ceramic materials. Paper was used
extensively in older devices and offers relatively high voltage performance. However, it is susceptible to water
absorption, and has been largely replaced by plastic film capacitors. Plastics offer better stability and aging
performance, which makes them useful in timer circuits, although they may be limited to low operating
temperatures and frequencies. Ceramic capacitors are generally small, cheap and useful for high frequency
applications, although their capacitance varies strongly with voltage and they age poorly. They are broadly
categorized as class 1 dielectrics, which have predictable variation of capacitance with temperature or class 2
dielectrics, which can operate at higher voltage. Glass and mica capacitors are extremely reliable, stable and tolerant
to high temperatures and voltages, but are too expensive for most mainstream applications. Electrolytic capacitors
and supercapacitors are used to store small and larger amounts of energy, respectively, ceramic capacitors are often
used in resonators, and parasitic capacitance occurs in circuits wherever the simple conductor-insulator-conductor
structure is formed unintentionally by the configuration of the circuit layout.
Electrolytic capacitors use an aluminum or tantalum plate with an oxide dielectric layer. The second electrode is a
liquid electrolyte, connected to the circuit by another foil plate. Electrolytic capacitors offer very high capacitance
but suffer from poor tolerances, high instability, gradual loss of capacitance especially when subjected to heat, and
high leakage current. Poor quality capacitors may leak electrolyte, which is harmful to printed circuit boards. The
conductivity of the electrolyte drops at low temperatures, which increases equivalent series resistance. While widely
used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for many
applications. Electrolytic capacitors will self-degrade if unused for a period (around a year), and when full power is
applied may short circuit, permanently damaging the capacitor and usually blowing a fuse or causing arcing in
rectifier tubes. They can be restored before use (and damage) by gradually applying the operating voltage, often
done on antique vacuum tube equipment over a period of 30 minutes by using a variable transformer to supply AC
power. Unfortunately, the use of this technique may be less satisfactory for some solid state equipment, which may
be damaged by operation below its normal power range, requiring that the power supply first be isolated from the
consuming circuits. Such remedies may not be applicable to modern high-frequency power supplies as these
produce full output voltage even with reduced input.
Tantalum capacitors offer better frequency and temperature characteristics than aluminum, but higher dielectric
absorption and leakage.[25]
12. Polymer capacitors (OS-CON, OC-CON) capacitors use solid conductive polymer (or polymerized organic
semiconductor) as electrolyte and offer longer life and lower ESR at higher cost than standard electrolytic capacitors.
A Feedthrough is a component that, while not serving as its main use, has capacitance and is used to conduct signals
through a circuit board.
Several other types of capacitor are available for specialist applications. Supercapacitors store large amounts of
energy. Supercapacitors made from carbon aerogel, carbon nanotubes, or highly porous electrode materials, offer
extremely high capacitance (up to 5 kF as of 2010) and can be used in some applications instead of rechargeable
batteries. Alternating current capacitors are specifically designed to work on line (mains) voltage AC power circuits.
They are commonly used in electric motor circuits and are often designed to handle large currents, so they tend to
be physically large. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed.
They also are designed with direct current breakdown voltages of at least five times the maximum AC voltage.
[edit]Structure
Capacitor packages: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right;
through-hole electrolytic at bottom right. Major scale divisions are cm.
The arrangement of plates and dielectric has many variations depending on the desired ratings of the capacitor. For
small values of capacitance (microfarads and less), ceramic disks use metallic coatings, with wire leads bonded to the
coating. Larger values can be made by multiple stacks of plates and disks. Larger value capacitors usually use a metal
foil or metal film layer deposited on the surface of a dielectric film to make the plates, and a dielectric film of
impregnated paper or plastic – these are rolled up to save space. To reduce the series resistance and inductance for
long plates, the plates and dielectric are staggered so that connection is made at the common edge of the rolled-up
plates, not at the ends of the foil or metalized film strips that comprise the plates.
The assembly is encased to prevent moisture entering the dielectric – early radio equipment used a cardboard tube
sealed with wax. Modern paper or film dielectric capacitors are dipped in a hard thermoplastic. Large capacitors for
high-voltage use may have the roll form compressed to fit into a rectangular metal case, with bolted terminals and
bushings for connections. The dielectric in larger capacitors is often impregnated with a liquid to improve its
properties.
Several axial-lead electrolytic capacitors.
Capacitors may have their connecting leads arranged in many configurations, for example axially or radially. "Axial"
means that the leads are on a common axis, typically the axis of the capacitor's cylindrical body – the leads extend
from opposite ends. Radial leads might more accurately be referred to as tandem; they are rarely actually aligned
along radii of the body's circle, so the term is inexact, although universal. The leads (until bent) are usually in planes
parallel to that of the flat body of the capacitor, and extend in the same direction; they are often parallel as
manufactured.
Small, cheap discoidal ceramic capacitors have existed since the 1930s, and remain in widespread use. Since the
1980s, surface mount packages for capacitors have been widely used. These packages are extremely small and lack
connecting leads, allowing them to be soldered directly onto the surface of printed circuit boards. Surface mount
13. components avoid undesirable high-frequency effects due to the leads and simplify automated assembly, although
manual handling is made difficult due to their small size.
Mechanically controlled variable capacitors allow the plate spacing to be adjusted, for example by rotating or sliding
a set of movable plates into alignment with a set of stationary plates. Low cost variable capacitors squeeze together
alternating layers of aluminum and plastic with a screw. Electrical control of capacitance is achievable with varactors
(or varicaps), which are reverse-biased semiconductor diodes whose depletion region width varies with applied
voltage. They are used in phase-locked loops, amongst other applications.
[edit]Capacitor markings
Most capacitors have numbers printed on their bodies to indicate their electrical characteristics. Larger capacitors
like electrolytics usually display the actual capacitance together with the unit (for example, 220 μF). Smaller
capacitors like ceramics, however, use a shorthand consisting of three numbers and a letter, where the numbers
show the capacitance in pF (calculated as XY × 10Z for the numbers XYZ) and the letter indicates the tolerance (J, K or
M for ±5%, ±10% and ±20% respectively).
Additionally, the capacitor may show its working voltage, temperature and other relevant characteristics.
[edit]Example
A capacitor with the text 473K 330V on its body has a capacitance of 47 × 103 pF = 47 nF (±10%) with a working
voltage of 330 V.
[edit]Applications
Main article: Applications of capacitors
This mylar-film, oil-filled capacitor has very low inductance and low resistance, to provide the high-power (70
megawatt) and high speed (1.2 microsecond) discharge needed to operate a dye laser.
[edit]Energy storage
A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary
battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being
changed. (This prevents loss of information in volatile memory.)
Conventional capacitors provide less than 360 joules per kilogram of energy density, whereas a conventional alkaline
battery has a density of 590 kJ/kg.
In car audio systems, large capacitors store energy for the amplifier to use on demand. Also for a flash tube a
capacitor is used to hold the high voltage.
[edit]Pulsed power and weapons
Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor banks) are used to supply
huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx
14. generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle
accelerators.
Large capacitor banks (reservoir) are used as energy sources for the exploding-bridgewire detonators or slapper
detonators in nuclear weapons and other specialty weapons. Experimental work is under way using banks of
capacitors as power sources for electromagnetic armour and electromagnetic railguns and coilguns.
[edit]Power conditioning
A 10 millifarad capacitor in an amplifier power supply
Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They
can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the
input voltage.
Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as
factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power
supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away
power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source,
and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor
compensates for the inductance and resistance of the leads to the lead-acid car battery.
[edit]Power factor correction
A high-voltage capacitor bank used for power factor correction on a power transmission system.
In electric power distribution, capacitors are used for power factor correction. Such capacitors often come as three
capacitors connected as a three phase load. Usually, the values of these capacitors are given not in farads but rather
as a reactive power in volt-amperes reactive (VAr). The purpose is to counteract inductive loading from devices like
electric motors and transmission lines to make the load appear to be mostly resistive. Individual motor or lamp loads
may have capacitors for power factor correction, or larger sets of capacitors (usually with automatic switching
devices) may be installed at a load center within a building or in a large utility substation.
[edit]Supression and coupling
[edit]Signal coupling
Main article: capacitive coupling
Polyester film capacitors are frequently used as coupling capacitors.
Because capacitors pass AC but block DC signals (when charged up to the applied dc voltage), they are often used to
separate the AC and DC components of a signal. This method is known as AC coupling or "capacitive coupling". Here,
15. a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the
signal frequency, is employed.
[edit]Decoupling
Main article: decoupling capacitor
A decoupling capacitor is a capacitor used to protect one part of a circuit from the effect of another, for instance to
suppress noise or transients. Noise caused by other circuit elements is shunted through the capacitor, reducing the
effect they have on the rest of the circuit. It is most commonly used between the power supply and ground. An
alternative name is bypass capacitor as it is used to bypass the power supply or other high impedance component of
a circuit.
[edit]Noise filters and snubbers
When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage
across the open circuit of the switch or relay. If the inductance is large enough, the energy will generate a spark,
causing the contact points to oxidize, deteriorate, or sometimes weld together, or destroying a solid-state switch. A
snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points,
thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. Similarly,
in smaller scale circuits, the spark may not be enough to damage the switch but will still radiate undesirable radio
frequency interference (RFI), which a filter capacitor absorbs. Snubber capacitors are usually employed with a low-
value resistor in series, to dissipate energy and minimize RFI. Such resistor-capacitor combinations are available in a
single package.
Capacitors are also used in parallel to interrupt units of a high-voltage circuit breaker in order to equally distribute
the voltage between these units. In this case they are called grading capacitors.
In schematic diagrams, a capacitor used primarily for DC charge storage is often drawn vertically in circuit diagrams
with the lower, more negative, plate drawn as an arc. The straight plate indicates the positive terminal of the device,
if it is polarized (see electrolytic capacitor).
[edit]Motor starters
Main article: motor capacitor
In single phase squirrel cage motors, the primary winding within the motor housing is not capable of starting a
rotational motion on the rotor, but is capable of sustaining one. To start the motor, a secondary "start" winding has
a series non-polarized starting capacitor to introduce a lead in the sinusoidal current. When the secondary (start)
winding is placed at an angle with respect to the primary (run) winding, a rotating electric field is created. The force
of the rotational field is not constant, but is sufficient to start the rotor spinning. When the rotor comes close to
operating speed, a centrifugal switch (or current-sensitive relay in series with the main winding) disconnects the
capacitor. The start capacitor is typically mounted to the side of the motor housing. These are called capacitor-
startmotors, that have relatively high starting torque. Typically they can have up-to four times as much starting
torque than a split-phase motor and are used on applications such as compressors, pressure washers and any small
device requiring high starting torques.
Capacitor-run induction motors have a permanently connected phase-shifting capacitor in series with a second
winding. The motor is much like a two-phase induction motor.
Motor-starting capacitors are typically non-polarized electrolytic types, while running capacitors are conventional
paper or plastic film dielectric types.
[edit]Signal processing
16. The energy stored in a capacitor can be used to represent information, either in binary form, as in DRAMs, or in
analogue form, as in analog sampled filters and CCDs. Capacitors can be used in analog circuits as components of
integrators or more complex filters and in negative feedback loop stabilization. Signal processing circuits also use
capacitors to integrate a current signal.
[edit]Tuned circuits
Capacitors and inductors are applied together in tuned circuits to select information in particular frequency bands.
For example, radio receivers rely on variable capacitors to tune the station frequency. Speakers use passive analog
crossovers, and analog equalizers use capacitors to select different audio bands.
The resonant frequency f of a tuned circuit is a function of the inductance (L) and capacitance (C) in series, and is
given by:
where L is in henries and C is in farads.
[edit]Sensing
Main article: capacitive sensing
Main article: Capacitive displacement sensor
Most capacitors are designed to maintain a fixed physical structure. However, various factors can change the
structure of the capacitor, and the resulting change in capacitance can be used to sense those factors.
Changing the dielectric:
The effects of varying the characteristics of the dielectric can be used for sensing purposes. Capacitors with an
exposed and porous dielectric can be used to measure humidity in air. Capacitors are used to accurately measure the
fuel level in airplanes; as the fuel covers more of a pair of plates, the circuit capacitance increases.
Changing the distance between the plates:
Capacitors with a flexible plate can be used to measure strain or pressure. Industrial pressure transmitters used for
process control use pressure-sensing diaphragms, which form a capacitor plate of an oscillator circuit. Capacitors are
used as the sensor in condenser microphones, where one plate is moved by air pressure, relative to the fixed
position of the other plate. Some accelerometers use MEMS capacitors etched on a chip to measure the magnitude
and direction of the acceleration vector. They are used to detect changes in acceleration, in tilt sensors, or to detect
free fall, as sensors triggering airbag deployment, and in many other applications. Some fingerprint sensors use
capacitors. Additionally, a user can adjust the pitch of a theremin musical instrument by moving his hand since this
changes the effective capacitance between the user's hand and the antenna.
Changing the effective area of the plates:
Capacitive touch switches are now used on many consumer electronic products.
[edit]Hazards and safety
17. Swollen caps of electrolytic capacitors - special design of semi-cut caps prevents capacitors from bursting
This high-energy capacitor from a defibrillator can deliver over 500 joules of energy. A resistor is connected between
the terminals for safety, to allow the stored energy to be released.
Catastrophic failure
Capacitors may retain a charge long after power is removed from a circuit; this charge can cause dangerous or even
potentially fatal shocks or damage connected equipment. For example, even a seemingly innocuous device such as a
disposable camera flash unit powered by a 1.5 volt AA battery contains a capacitor which may be charged to over
300 volts. This is easily capable of delivering a shock. Service procedures for electronic devices usually include
instructions to discharge large or high-voltage capacitors, for instance using a Brinkley stick. Capacitors may also
have built-in discharge resistors to dissipate stored energy to a safe level within a few seconds after power is
removed. High-voltage capacitors are stored with the terminals shorted, as protection from potentially dangerous
voltages due to dielectric absorption.
Some old, large oil-filled paper or plastic film capacitors contain polychlorinated biphenyls (PCBs). It is known that
waste PCBs can leak into groundwater under landfills. Capacitors containing PCB were labelled as containing
"Askarel" and several other trade names. PCB-filled paper capacitors are found in very old (pre-1975) fluorescent
lamp ballasts, and other applications.
Capacitors may catastrophically fail when subjected to voltages or currents beyond their rating, or as they reach
their normal end of life. Dielectric or metal interconnection failures may create arcing that vaporizes the dielectric
fluid, resulting in case bulging, rupture, or even an explosion. Capacitors used in RF or sustained high-current
applications can overheat, especially in the center of the capacitor rolls. Capacitors used within high-energy
capacitor banks can violently explode when a short in one capacitor causes sudden dumping of energy stored in the
rest of the bank into the failing unit. High voltage vacuum capacitors can generate soft X-rays even during normal
operation. Proper containment, fusing, and preventive maintenance can help to minimize these hazards.
High-voltage capacitors can benefit from a pre-charge to limit in-rush currents at
power-up of high voltage direct current (HVDC) circuits. This will extend the life of the
component and may mitigate high-voltage hazards.