romikgosai/squad_modified huggingface dataset:
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.

Questions and answers:
['
Q: What name is given to the AC component of an applied source having either constant or alternating frequency?
A: Ripple current', '
Q: What is one cause of dielectric losses in a capacitor?
A: changing field strength', '
Q: What is another cause of dielectric losses in a capacitor?
A: current flow across the slightly resistive supply lines or the electrolyte', '
Q: 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?
A: equivalent series resistance (ESR)', '
Q: What is one type of capacitor that has a specified rating value for maximum ripple current?
A: aluminum electrolytic capacitors']
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.

Questions and answers:
['
Q: What value of some capacitors decreases with age?
A: The capacitance', '
Q: What causes the decrease of capacitance in ceramic capacitors as they age?
A: degradation of the dielectric', '
Q: What is one of the most important aging factors in capacitors?
A: The type of dielectric', '
Q: What is another important factor which governs how a capacitor ages?
A: ambient operating and storage temperatures', '
Q: At what point can the aging effect of a capacitor be reversed if the component is heated beyond?
A: the Curie point']
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.

Questions and answers:
['
Q: What is the effect called when capacitors absorb sound waves?
A: microphonic effect', '
Q: What value of a capacitor is varied when vibration moves the conducting plates? 
A: the capacitance', '
Q: What sort of current is induced when the capacitance of a capacitor is altered?
A: AC current', '
Q: In what type of applications is piezeoelectricity especially problematic?
A: audio applications', '
Q: What is it called when a changing electric field existing between the conductive plates of a capacitor physically moves them?
A: the reverse microphonic effect']
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.

Questions and answers:
['
Q: What is one type of circuit in which voltage and current reversal are affected by damping?
A: DC circuits', '
Q: What is another type of circuit in which voltage and current reversal are affected by damping?
A: pulsed circuits', '
Q: Under what condition does voltage reversal occur in RLC circuits?
A: under-damped', '
Q: What is formed between the inductance and the capacitance when the current and the voltage switch direction?
A: a harmonic oscillator', '
Q: When a system is over-damped, what does it typically not experience?
A: a voltage reversal']
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.

Questions and answers:
['
Q: What percentage of voltage reversal does an AC circuit experience?
A: 100% voltage reversal', '
Q: What does voltage reversal create in the dielectric of a capacitor?
A: excess electric fields', '
Q: What percentage of voltage reversal will an under damped DC circuit experience?
A: less than 100%', '
Q: What does excess electric field present in the dielectric lead to?
A: heating of both the dielectric and the conductors', '
Q: When designing a capacitor, what is an important rating to consider?
A: Reversal ratings']
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.

Questions and answers:
['
Q: After discharging and disconnecting a capacitor, what causes it to develop a voltage?
A: hysteresis in the dielectric', '
Q: What does the process of dielectric absorption in a capacitor depend on?
A: time-dependent', '
Q: What level of dielectric absorption would a tantalum electrolytic capacitor display? 
A: very high absorption', '
Q: What level of dielectric absorption would a Teflon capacitor exhibit?
A: very small levels of absorption', '
Q: What amount of energy must a capacitor contain in order to be generally considered dangerous? 
A: over 10 joules of energy']
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.

Questions and answers:
['
Q: With what value is a resistor in parallel with a capacitor equal to?
A: Leakage', '
Q: What can cause excessive leakage in a capacitor?
A: Constant exposure to heat', '
Q: 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?
A: interstage coupling capacitors', '
Q: What type of capacitor can cause signal distortion in the downstream tube?
A: A leaky capacitor', '
Q: If the grid circuit voltage is increased beyond its regular bias setting, what can happen to the conductive plates in power amplifiers?
A: cause the plates to glow red']
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.

Questions and answers:
['
Q: What do many capacitors contain that raises the capacitance?
A: a dielectric spacer', '
Q: What sort of dielectric is used in low capacitance devices?
A: a vacuum', '
Q: What sort of capacitors have traditionally been used in radio tuning circuits?
A: Variable capacitors', '
Q: How did the capacitor traditionally used in radio tuning circuits change over time? 
A: use polymer foil dielectric between the moving and stationary plates', '
Q: What did the later designs of capacitors used in radio tuning circuits no longer have?
A: no significant air space']
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.

Questions and answers:
['
Q: What benefit is offered by solid state paper capacitors?
A: relatively high voltage performance', '
Q: What type of capacitor has mostly replaced solid state paper capacitors?
A: plastic film capacitors', '
Q: What sort of circuit are plastic capacitors especially useful for?
A: timer circuits', '
Q: What is one type of reliable capacitor that is resistant to temperature and voltage changes?
A: Glass', '
Q: What is another type of reliable capacitor that is resistant to temperature and voltage changes?
A: mica capacitors']
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.

Questions and answers:
['
Q: What is one type of metal which the conducting plates in electrolytic capacitors are commonly made of?
A: aluminum', '
Q: What type of dielectric layer is used in electrolytic capacitors?
A: an oxide dielectric layer', '
Q: What happens to the conductivity of the electrolyte at low temperatures?
A: drops at low temperatures', '
Q: How can electrolytic capacitors be safely used after having been stored unused for a long time?
A: by gradually applying the operating voltage', '
Q: Why might the method gradually applying the operating voltage not be suitable to protect electrolytic capacitors in modern devices?
A: these produce full output voltage even with reduced input']
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.

Questions and answers:
['
Q: What is the main feature of a supercapacitor?
A: Supercapacitors store large amounts of energy', '
Q: What is one type of material with which a supercapacitor may be constructed?
A: carbon nanotubes', '
Q: As of 2010, what is the highest capacitance a supercapacitor has achieved?
A: up to 5 kF', '
Q: What type of capacitor is commonly used in electric motor circuits?
A: Alternating current capacitors', '
Q: How many times the maximum AC voltage are AC capacitors designed to withstand?
A: at least five times the maximum AC voltage']
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):

Questions and answers:
['
Q: Under what condition might the polarization of the dielectric be unable to follow the voltage?
A: driven with a time-varying voltage that changes rapidly', '
Q: What type of dipoles which add to the dielectric constant cannot move instantly if a rapidly changing time varying voltage is driving the capacitor?
A: the internal microscopic dipoles', '
Q: What is it called when a dielectric constant changes with frequency?
A: dielectric dispersion', '
Q: What regulates dielectric dispersion?
A: dielectric relaxation processes', '
Q: What is an example of a dielectric relaxation process?
A: Debye relaxation']
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.)

Questions and answers:
['
Q: How is the complex impedance with dielectric represented mathematically?
A: Z(ω)', '
Q: How is the complex capacitance without dielectric represented mathematically?
A: C0', '
Q: Why is the value of C0 unattainable in reality?
A: even the quantum vacuum is predicted to exhibit nonideal behavior', '
Q: Under what condition is the approximation C0 sufficiently accurate for calculation purposes?
A: in terrestrial vacuum', '
Q: How is the complex capacitance mathematically represented with the dielectric present?
A: Ccmplx(ω)']
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.

Questions and answers:
['
Q: What order of magnitude of capacitance is suitable for capacitors comprised of ceramic disks with metallic coatings?
A: microfarads and less', '
Q: How are larger value capacitors often constructed?
A: multiple stacks of plates and disks', '
Q: What do larger value capacitors often use as the dielectric medium?
A: impregnated paper or plastic – these are rolled up to save space', '
Q: Why are the plates and dielectrics often staggered in larger value capacitors?
A: To reduce the series resistance and inductance', '
Q: How are the conductive plates often made for larger value capacitors?
A: metal film layer deposited on the surface of a dielectric film']
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.

Questions and answers:
['
Q: What is one type of configuration in which a capacitor may have its connecting leads organized?
A: axially', '
Q: What is another type of configuration in which a capacitor may have its connecting leads arranged?
A: radially', '
Q: Which type of configuration is often manufactured with the leads parallel to the body of the capacitor?
A: Radial', '
Q: How are the leads of an axially configured capacitor arranged?
A: on a common axis', '
Q: How could radial leads be more correctly described?
A: as tandem']
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.

Questions and answers:
['
Q: Since when have inexpensive ceramic disc capacitors existed?
A: the 1930s', '
Q: Since when have surface mount packages for capacitors been commonly in use?
A: the 1980s', '
Q: What do surface mount packages lack that allows their use on the surface of printed circuit boards?
A: connecting leads', '
Q: What is one benefit of using surface mount components?
A: simplify automated assembly', '
Q: What is one difficulty when using surface mount components?
A: 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.

Questions and answers:
['
Q: What do mechanically controlled variable capacitors enable to be modified?
A: the plate spacing', '
Q: How do cheap variable capacitors vary the separation distance between layers of a plastic and aluminum?
A: with a screw', '
Q: Of what type of diodes are varactors or varicaps comprised?
A: reverse-biased semiconductor diodes', '
Q: What varies as a function of voltage in varactors?
A: depletion region', '
Q: What is an application of varactors?
A: phase-locked loops']