What Is the Net Charge of a Capacitor?

Structure of a Capacitor

• Capacitors are constructed of two conductive surfaces, separated by an insulating material known as a dielectric. The dielectric isolates the plates, so that no current can flow between them. Capacitors can come in many shapes, but the standard form consists of two parallel plates for the conductors, separated by ceramic, polystyrene, or oil for the dielectric. The conductors and insulator are encased in a protective cover, usually made of ceramic or metal.

Capacitance

• The dielectric prevents current from flowing through a capacitor, instead allowing it to store built up charge. Capacitance is determined by the charge of the positive conductor, divided by the voltage of the capacitor's energy source. The standard unit of capacitance is the farad, and most capacitors used in electronics are measured in smaller units called microfarads or picofarads. While you can use the charge of one of the plates to find capacitance, this is different from the net charge of the capacitor.

Net Charge

• While its plates are used to store charges of varying magnitudes, the net charge of a capacitor as a whole is always zero. After the capacitor is charged, each plate carries an electric charge that is equal and opposite the charge of the other. When one plate carries a positive charge, the other plate carries a negative charge of the same magnitude, so the positive and negative charges balance out to a net charge of zero.

Types of Capacitors

• Two main categories of capacitors exist, polarized and unpolarized. Polarized capacitors have designated positive and negative leads. Their capacitance ratings are greater than unpolarized capacitors, starting at one microfarad. Unpolarized capacitors, on the other hand, have larger voltage ratings than polarized capacitors, but capacitance ratings less than one microfarad.