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Lecture 28 - LC, RLC circuits

# Lecture 28 - LC, RLC circuits - Energy in E and B fields...

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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 0 . What happens when switch is closed? Current starts at ( ) 0 0 C V Q I R RC + = = And then decays: ( ) 0 t Q I t e RC RC τ τ = = t I 0 Q RC Current through R t Q 0 Q Charge in capacitor t U 2 0 2 Q C Energy in capacitor RL circuit + + − − C L Capacitor is initially charged with Q 0 . 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 charge on the bottom plate.

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