rajpurkar/squad huggingface dataset:
Title: Capacitor

 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.

Question: What characteristic can leakage current and parasitic effects be assumed to have in the equation for a realistic capacitor?
Answer: can be assumed to be linear

Question: What sort of components can be added to the equivalent circuit of a capacitor in order to deal with leakage current and parasitic effects?
Answer: virtual components

Question: Upon dealing with leakage current and parasitic effects in a realistic model of a capacitor, what sort of methods can then be applied?
Answer: The usual methods of network analysis

Question: What sort of analysis cannot be used in cases of voltage breakdown in modelling a capacitor?
Answer: normal (i.e., linear) network analysis cannot be used

Question: What causes the assumption of constant capacitance to fail even if the effect is linear in nature?
Answer: temperature dependence
Title: Capacitor

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; it can be much less when other materials are used for the dielectric. 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 and causing a short (or relatively low resistance) circuit. The results can be explosive as the short in the capacitor draws current from the surrounding circuitry and dissipates the energy.

Question: What order is the breakdown field strength for air dielectric capacitors of?
Answer: of the order 2 to 5 MV/m

Question: Of what order is the breakdown field strength for mica dielectric capacitors?
Answer: 100 to 300 MV/m

Question: In what way is the dielectric used in order to cause the absolute breakdown voltage of capacitors to be limited?
Answer: The dielectric is used in very thin layers

Question: What is one factor that critically affects the breakdown voltage of the capacitor?
Answer: the geometry of the capacitor conductive parts

Question: What is the difference in the physical attributes of the dielectric used in high voltage capacitors compared to low voltage capacitors?
Answer: the dielectric must be thicker
Title: Capacitor

Ripple current is the AC component of an applied source (often a switched-mode power supply) whose frequency may be constant or varying. Ripple current causes heat to be generated within the capacitor due to the dielectric losses caused by the changing field strength together with the current flow across the slightly resistive supply lines or the electrolyte in the capacitor. The equivalent series resistance (ESR) is the amount of internal series resistance one would add to a perfect capacitor to model this. Some types of capacitors, primarily tantalum and aluminum electrolytic capacitors, as well as some film capacitors have a specified rating value for maximum ripple current.

Question: What name is given to the AC component of an applied source having either constant or alternating frequency?
Answer: Ripple current

Question: What is one cause of dielectric losses in a capacitor?
Answer: changing field strength

Question: What is another cause of dielectric losses in a capacitor?
Answer: current flow across the slightly resistive supply lines or the electrolyte

Question: What is the name given to the amount of internal series resistance needed to add to an ideal capacitor model in order to represent the heat generated by dielectric losses?
Answer: equivalent series resistance (ESR)

Question: What is one type of capacitor that has a specified rating value for maximum ripple current?
Answer: aluminum electrolytic capacitors
Title: Capacitor

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. Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component.

Question: What value of some capacitors decreases with age?
Answer: The capacitance

Question: What causes the decrease of capacitance in ceramic capacitors as they age?
Answer: degradation of the dielectric

Question: What is one of the most important aging factors in capacitors?
Answer: The type of dielectric

Question: What is another important factor which governs how a capacitor ages?
Answer: ambient operating and storage temperatures

Question: At what point can the aging effect of a capacitor be reversed if the component is heated beyond?
Answer: the Curie point
Title: Capacitor

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.

Question: What is the effect called when capacitors absorb sound waves?
Answer: microphonic effect

Question: What value of a capacitor is varied when vibration moves the conducting plates? 
Answer: the capacitance

Question: What sort of current is induced when the capacitance of a capacitor is altered?
Answer: AC current

Question: In what type of applications is piezeoelectricity especially problematic?
Answer: audio applications

Question: What is it called when a changing electric field existing between the conductive plates of a capacitor physically moves them?
Answer: the reverse microphonic effect
Title: Capacitor

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.

Question: What is one type of circuit in which voltage and current reversal are affected by damping?
Answer: DC circuits

Question: What is another type of circuit in which voltage and current reversal are affected by damping?
Answer: pulsed circuits

Question: Under what condition does voltage reversal occur in RLC circuits?
Answer: under-damped

Question: What is formed between the inductance and the capacitance when the current and the voltage switch direction?
Answer: a harmonic oscillator

Question: When a system is over-damped, what does it typically not experience?
Answer: a voltage reversal
Title: Capacitor

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.

Question: What percentage of voltage reversal does an AC circuit experience?
Answer: 100% voltage reversal

Question: What does voltage reversal create in the dielectric of a capacitor?
Answer: excess electric fields

Question: What percentage of voltage reversal will an under damped DC circuit experience?
Answer: less than 100%

Question: What does excess electric field present in the dielectric lead to?
Answer: heating of both the dielectric and the conductors

Question: When designing a capacitor, what is an important rating to consider?
Answer: Reversal ratings
Title: Capacitor

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?
Answer: hysteresis in the dielectric

Question: What does the process of dielectric absorption in a capacitor depend on?
Answer: time-dependent

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

Question: What level of dielectric absorption would a Teflon capacitor exhibit?
Answer: very small levels of absorption

Question: What amount of energy must a capacitor contain in order to be generally considered dangerous? 
Answer: over 10 joules of energy
Title: Capacitor

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?
Answer: Leakage

Question: What can cause excessive leakage in a capacitor?
Answer: Constant exposure to heat

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?
Answer: interstage coupling capacitors

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

Question: If the grid circuit voltage is increased beyond its regular bias setting, what can happen to the conductive plates in power amplifiers?
Answer: cause the plates to glow red
Title: Capacitor

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?
Answer: a dielectric spacer

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

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

Question: How did the capacitor traditionally used in radio tuning circuits change over time? 
Answer: use polymer foil dielectric between the moving and stationary plates

Question: What did the later designs of capacitors used in radio tuning circuits no longer have?
Answer: no significant air space
Title: Capacitor

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?
Answer: relatively high voltage performance

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

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

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

Question: What is another type of reliable capacitor that is resistant to temperature and voltage changes?
Answer: mica capacitors
Title: Capacitor

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?
Answer: aluminum

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

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

Question: How can electrolytic capacitors be safely used after having been stored unused for a long time?
Answer: by gradually applying the operating voltage

Question: Why might the method gradually applying the operating voltage not be suitable to protect electrolytic capacitors in modern devices?
Answer: these produce full output voltage even with reduced input
Title: Capacitor

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?
Answer: Supercapacitors store large amounts of energy

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

Question: As of 2010, what is the highest capacitance a supercapacitor has achieved?
Answer: up to 5 kF

Question: What type of capacitor is commonly used in electric motor circuits?
Answer: Alternating current capacitors

Question: How many times the maximum AC voltage are AC capacitors designed to withstand?
Answer: at least five times the maximum AC voltage
Title: Capacitor

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?
Answer: driven with a time-varying voltage that changes rapidly

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?
Answer: the internal microscopic dipoles

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

Question: What regulates dielectric dispersion?
Answer: dielectric relaxation processes

Question: What is an example of a dielectric relaxation process?
Answer: Debye relaxation
Title: Capacitor

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?
Answer: Z(ω)

Question: How is the complex capacitance without dielectric represented mathematically?
Answer: C0

Question: Why is the value of C0 unattainable in reality?
Answer: even the quantum vacuum is predicted to exhibit nonideal behavior

Question: Under what condition is the approximation C0 sufficiently accurate for calculation purposes?
Answer: in terrestrial vacuum

Question: How is the complex capacitance mathematically represented with the dielectric present?
Answer: Ccmplx(ω)