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Unformatted text preview: Lecture 28 LC and RLC circuits. Energy in E and B fields Energy stored in a capacitor + + + + + + E 2 1 2 U CV = energy of the electric field 2 1 2 U LI = Energy stored in a inductor B energy of the magnetic field RC circuits (review) + + C R Capacitor is initially charged with Q . What happens when switch is closed? Current starts at ( ) C V Q I R RC + = = And then decays: ( ) t Q I t e RC RC = = t I Q RC Current through R t Q Q Charge in capacitor t U 2 2 Q C Energy in capacitor RL circuit + + C L Capacitor is initially charged with Q . What happens when switch is closed? Right after it is closed: I = 0. Then current builds up. Magnetic field is created in inductor while charge in capacitor is decreasing Energy is being transferred form C to L (from electric to magnetic energy) As C discharges, current should decrease and stop, but inductor keeps it going, so at the end the capacitor is charged again but with the positive...
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