sentence-transformers/squad huggingface dataset:
Passage: Capacitors made with any type of dielectric material will show some level of "dielectric absorption" or "soakage". On discharging a capacitor and disconnecting it, after a short time it may develop a voltage due to hysteresis in the dielectric. This effect can be objectionable in applications such as precision sample and hold circuits or timing circuits. The level of absorption depends on many factors, from design considerations to charging time, since the absorption is a time-dependent process. However, the primary factor is the type of dielectric material. Capacitors such as tantalum electrolytic or polysulfone film exhibit very high absorption, while polystyrene or Teflon allow very small levels of absorption. In some capacitors where dangerous voltages and energies exist, such as in flashtubes, television sets, and defibrillators, the dielectric absorption can recharge the capacitor to hazardous voltages after it has been shorted or discharged. Any capacitor containing over 10 joules of energy is generally considered hazardous, while 50 joules or higher is potentially lethal. A capacitor may regain anywhere from 0.01 to 20% of its original charge over a period of several minutes, allowing a seemingly safe capacitor to become surprisingly dangerous.

Question: After discharging and disconnecting a capacitor, what causes it to develop a voltage?

Question: What does the process of dielectric absorption in a capacitor depend on?

Question: What level of dielectric absorption would a tantalum electrolytic capacitor display?

Question: What level of dielectric absorption would a Teflon capacitor exhibit?

Question: What amount of energy must a capacitor contain in order to be generally considered dangerous?
Passage: 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.

Question: With what value is a resistor in parallel with a capacitor equal to?

Question: What can cause excessive leakage in a capacitor?

Question: What sort of capacitors are used to carry a varying signal from the conductive plate of one tube to the grid circuit of the next stage?

Question: What type of capacitor can cause signal distortion in the downstream tube?

Question: If the grid circuit voltage is increased beyond its regular bias setting, what can happen to the conductive plates in power amplifiers?
Passage: 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.

Question: What do many capacitors contain that raises the capacitance?

Question: What sort of dielectric is used in low capacitance devices?

Question: What sort of capacitors have traditionally been used in radio tuning circuits?

Question: How did the capacitor traditionally used in radio tuning circuits change over time?

Question: What did the later designs of capacitors used in radio tuning circuits no longer have?
Passage: 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 ageing 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.

Question: What benefit is offered by solid state paper capacitors?

Question: What type of capacitor has mostly replaced solid state paper capacitors?

Question: What sort of circuit are plastic capacitors especially useful for?

Question: What is one type of reliable capacitor that is resistant to temperature and voltage changes?

Question: What is another type of reliable capacitor that is resistant to temperature and voltage changes?
Passage: 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 failure of rectifier diodes (for instance, in older equipment, 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.

Question: What is one type of metal which the conducting plates in electrolytic capacitors are commonly made of?

Question: What type of dielectric layer is used in electrolytic capacitors?

Question: What happens to the conductivity of the electrolyte at low temperatures?

Question: How can electrolytic capacitors be safely used after having been stored unused for a long time?

Question: Why might the method gradually applying the operating voltage not be suitable to protect electrolytic capacitors in modern devices?
Passage: 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[update]) 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.

Question: What is the main feature of a supercapacitor?

Question: What is one type of material with which a supercapacitor may be constructed?

Question: As of 2010, what is the highest capacitance a supercapacitor has achieved?

Question: What type of capacitor is commonly used in electric motor circuits?

Question: How many times the maximum AC voltage are AC capacitors designed to withstand?
Passage: If a capacitor is driven with a time-varying voltage that changes rapidly enough, at some frequency the polarization of the dielectric cannot follow the voltage. As an example of the origin of this mechanism, the internal microscopic dipoles contributing to the dielectric constant cannot move instantly, and so as frequency of an applied alternating voltage increases, the dipole response is limited and the dielectric constant diminishes. A changing dielectric constant with frequency is referred to as dielectric dispersion, and is governed by dielectric relaxation processes, such as Debye relaxation. Under transient conditions, the displacement field can be expressed as (see electric susceptibility):

Question: Under what condition might the polarization of the dielectric be unable to follow the voltage?

Question: What type of dipoles which add to the dielectric constant cannot move instantly if a rapidly changing time varying voltage is driving the capacitor?

Question: What is it called when a dielectric constant changes with frequency?

Question: What regulates dielectric dispersion?

Question: What is an example of a dielectric relaxation process?
Passage: where a single prime denotes the real part and a double prime the imaginary part, Z(ω) is the complex impedance with the dielectric present, Ccmplx(ω) is the so-called complex capacitance with the dielectric present, and C0 is the capacitance without the dielectric. (Measurement "without the dielectric" in principle means measurement in free space, an unattainable goal inasmuch as even the quantum vacuum is predicted to exhibit nonideal behavior, such as dichroism. For practical purposes, when measurement errors are taken into account, often a measurement in terrestrial vacuum, or simply a calculation of C0, is sufficiently accurate.)

Question: How is the complex impedance with dielectric represented mathematically?

Question: How is the complex capacitance without dielectric represented mathematically?

Question: Why is the value of C0 unattainable in reality?

Question: Under what condition is the approximation C0 sufficiently accurate for calculation purposes?

Question: How is the complex capacitance mathematically represented with the dielectric present?
Passage: 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.

Question: What order of magnitude of capacitance is suitable for capacitors comprised of ceramic disks with metallic coatings?

Question: How are larger value capacitors often constructed?

Question: What do larger value capacitors often use as the dielectric medium?

Question: Why are the plates and dielectrics often staggered in larger value capacitors?

Question: How are the conductive plates often made for larger value capacitors?
Passage: 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.

Question: What is one type of configuration in which a capacitor may have its connecting leads organized?

Question: What is another type of configuration in which a capacitor may have its connecting leads arranged?

Question: Which type of configuration is often manufactured with the leads parallel to the body of the capacitor?

Question: How are the leads of an axially configured capacitor arranged?

Question: How could radial leads be more correctly described?
Passage: 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 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.

Question: Since when have inexpensive ceramic disc capacitors existed?

Question: Since when have surface mount packages for capacitors been commonly in use?

Question: What do surface mount packages lack that allows their use on the surface of printed circuit boards?

Question: What is one benefit of using surface mount components?

Question: What is one difficulty when using surface mount components?
Passage: 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.

Question: What do mechanically controlled variable capacitors enable to be modified?

Question: How do cheap variable capacitors vary the separation distance between layers of a plastic and aluminum?

Question: Of what type of diodes are varactors or varicaps comprised?

Question: What varies as a function of voltage in varactors?

Question: What is an application of varactors?
Passage: 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 numeric digits and a letter, where the digits indicate the capacitance in pF (calculated as XY × 10Z for digits XYZ) and the letter indicates the tolerance (J, K or M for ±5%, ±10% and ±20% respectively).

Question: How do larger capacitors present their electrical characteristics?

Question: What does the abbreviated electrical characteristics of smaller capacitors consist of?

Question: What part of the electrical characteristics of smaller capacitors do the digits of the abbreviated notation represent ?

Question: What does the letter of the abbreviated notation for the electrical characteristics of smaller capacitors represent?

Question: In what SI unit is the capacitance reported on smaller capacitors?
Passage: 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.

Question: Why are capacitors connected in parallel with the power circuits of many devices and large systems?

Question: How do the capacitors connected in parallel act with currents from the power supply?

Question: What is one value a stiffening capacitor accounts for when used in for car audio purposes?

Question: What is another value a stiffening capacitor accounts for when used in for car audio purposes?

Question: What do parallel capacitors do to fluctuating current in order to deliver "clean" power for control circuits?
Passage: 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.

Question: In what scenario are capacitors used for power factor correction?

Question: How are capacitors used for for power factor correction prepared?

Question: In what what unit is the capacitance reported for capacitors used in power factor correction?

Question: What is the reason for using capacitors in power factor correction?

Question: How are power factor correction capacitors sometimes installed?
Passage: 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.

Question: What happens to the current when an inductive circuit is opened?

Question: What happens to the voltage when an inductive circuit is opened?

Question: What type of capacitor is used to make a path to bypass the contact points?

Question: What is a typical system in which a snubber capacitor is found?

Question: What type of capacitor absorbs radio frequency interference?
Passage: 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-start motors, 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.

Question: What is the main winding on a squirrel cage motor capable of withstanding?

Question: What sort of capacitors are used on the second winding of a squirrel cage motor?

Question: What does the capacitor on the second winding of a squirrel cage motor do?

Question: What does the centrifugal switch do the capacitor when the rotor achieves operating speed?

Question: Where is the start capacitor commonly mounted?
Passage: 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, has a capacitor which may contain over 15 joules of energy and 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 or from transient voltages the capacitor may pick up from static charges or passing weather events.

Question: How much energy could a capacitor in a disposable camera contain?

Question: To what voltage could a capacitor from a disposable camera be charged to?

Question: What device can be used to discharge large voltage capacitors?

Question: How are the terminals of high voltage capacitors stored?

Question: What type of charge could a capacitor pick up a transient charge from?
Passage: 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.

Question: What could cause the failure of a capacitor?

Question: What can happen to capacitors used in high current applications?

Question: What can happen to capacitors used in high energy capacitor banks?

Question: What type of capacitors can generate soft x-rays?

Question: What is one way to help minimize capacitor dangers?