Lecture 13 - Energy storage and dielectrics

Lecture 13 - Energy storage and dielectrics - 1 Lecture 13...

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Unformatted text preview: 1 Lecture 13 Electric energy Capacitors with dielectrics Energy stored in a capacitor Work to add a charge d q to a capacitor with capacitance C and charge q : ext electric dW dW = external work needed to charge it dU Vdq q dq C Q ext q W d q C Total work: Energy stored in a capacitor 2 2 1 1 2 2 2 Q U C V Q V C DEMOs: Discharge of a capacitor through a bulb Capacitors store BIG energy. C 2 2 Q C ACT: Variable capacitor (II) A parallel plate capacitor is connected to a battery. While still connected, the distance between the plates is halved. Due to this, the energy stored in the capacitor: A C d d → d /2 A. Increases B. Decreases C. Stays the same C → 2 C V is constant, 2 1 2 U C V U → 2 U ACT: Variable capacitor (III) A parallel plate capacitor is connected to a battery. After it is charged, we disconnect it. Then the distance between the plates is halved. Due to this, the energy stored in the capacitor: A C d d → d /2 A. Increases B. Decreases C. Stays the same C → 2 C Q is constant, 2 1 2 Q U C U → U/2 2 Where is the energy stored?Where is the energy stored?...
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This note was uploaded on 09/21/2011 for the course PHYS 222 taught by Professor Johnson during the Spring '07 term at Iowa State.

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Lecture 13 - Energy storage and dielectrics - 1 Lecture 13...

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