History, Theory, and Applications of Capacitors :: capacitor electronics

Static electricity was discovered in 600 B.C., but it was not until the mid 1700's when energy storage properties were discovered. 'With the discovery of the first Leyden jar, it was referred to as a condenser because electricity was thought of as a fluid which could condense. The Lehden jar is a glass partially filled with water that has a wire inserted through the top of an insulating stopper (cork). When the wire is charged by static electricity, it holds the charge until the wire comes into contact with a conductor which will discharge the glass. It was roughly one hundred years later when Michael Faraday discovered a variable capacitor. He did this by measuring the varying capacitance of different dielectrics on capacitor.'(4) When the first aluminum capacitor was discovered, some thirty years after Faraday's work, the SI unit used measuring capacitance was named a farad (F) in his honor. 1F = 1 C / V In words: one Farad is equal to one Coulomb per Volt Since the farad is a large unit of capacitance, most capacitors have units of picofarads (pF) or nanofarads (nF). To this day only one type of capacitor has the ability to store enough energy to warrant measurements using a farad as the standard unit, and this is the super capacitor. A capacitor consists of two conducting surfaces separated by an insulator (dielectric). The value of capacitance depends not only on the geometry of the capacitor, but the dielectric as well. (1) "Since capacitance (C) of a capacitor is the ratio of the magnitude of the charge on either conductor to the magnitude of the potential difference (V) between them: " (1) : When a DC voltage source is applied to the 10 mF capacitor shown to the left, a charge is stored on each side of the electrode. A mulitmeter is used to measure resistance, it is shown that when the capacitor is charging, current is moving and when the capacitor is fully charged, the current will stop flowing, because there is no change in electric potenial, so the resistance goes to zero. You can see that when the electodes are switched, the resistance again goes to zero when the capacitor is fully charged. AC current is allowed to pass through the conductor continuously because it works similiar to the way the probes are switching, so the current is allowed continuos flow. The main function of a capacitor is for it to store energy and to act as a filter, passing current (AC) and blocking current (DC).