the purpose of a dielectric material used in a capacitor is as an insulator.
what is the purpose of a dielectric material used in a capacitor?
insulator
gradual loss of energy from a charged capacitor is primarily caused by electronic devices attached to the capacitors, such as transistors or diodes, which conduct a small amount of current even when they are turned off. even though this off current is an order of magnitude less than the current through the device when it is on, the current still slowly discharges the capacitor. another contributor to leakage from a capacitor is from the undesired imperfection of some dielectric materials used in capacitors, also known as "dielectric leakage". it is a result of the dielectric material not being a perfect insulator and having some non-zero conductivity, allowing a "leakage current" to flow, slowly discharging the capacitor.
leakage (electronics)
capacitors made with any type of dielectric material 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 is 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 relatively 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.
capacitor