Thisbeginswiththestructureofthecapacitor.Thesimplestcapacitorsaremadeupofpolarplatesatbothendsandinsulatingdielectric(includingair)atthemiddle.Afterelectrification,theplateischarged,formingavoltage(potentialdifference),butbecauseoftheintermediateinsulation,theentirecapacitorisnon-conductive.However,theconditionisthatthecriticalvoltage(breakdownvoltage)ofthecapacitorisnotexceeded.Weknowthatanysubstanceisrelativelyinsulated,andwhenthevoltageatbothendsofthematerialincreasestoacertainextent,thematerialcanconductelectricity.Wecallthisvoltageabreakdownvoltage.Capacitanceisnoexception.Whenthecapacitorisbroken,itisnotaninsulator.Inmiddleschool,however,suchvoltagesareinvisibleincircuits,sotheyworkbelowbreakdownvoltagesandcanbetreatedasinsulators.)