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Energy Density Leyden Jar A Leyden jar has metal foil on both the inside and outside surface. The surfaces are connected each to a voltage source. The electrical energy is stored • • • • A) nowhere since there the charges are static. B) on the metal foil. C) in the glass of the jar. D) in the space inside the jar. Work Between Moving a charge from one + - plate of a capacitor to another requires work. • Move positives from negative plate + As more charge moves the field increases • So does work needed + The average work needed is equal to energy stored. W 1 1 CV 2 Q 2 / C 2 2 - W 1 QV 2 Total Energy Q C1V + C2V The energy stored in a system C1 + - Q1 C1V of capacitors can be determined from the energy stored in each E1 12 C1V 2 E2 12 C2V 2 C2 Q2 C2V E 12 C1V 2 + 12 C2V 2 E + - 1 2 C1 + C2 V 2 Open Circuit A charged capacitor will hold the charge unless there is a path for the charge to move freely. If the wires are disconnected this is an open circuit. + - Closed Circuit A wire connecting the plates forms a conducting path. This is a closed circuit. • Also called a short circuit A short circuit releases the energy stored in the capacitor. • Sudden release can cause unwanted surges of charge + -