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Unformatted text preview: at high voltage) (affordable) PHY2049: Chapter 25 19 Dielectric Mechanism is Due to Polarization E = 0, Dipoles randomly aligned E applied, partially aligns dipoles Aligned dipoles induce surface charges Surface charges partially cancel E field Yow! http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dielec.html PHY2049: Chapter 25 20 ConcepTest Two identical capacitors are given the same charge Q, then disconnected from a battery. After C2 has been charged and disconnected it is filled with a dielectric. Compare the voltages of the two capacitors. Voltage lowered to V/κ (1) V1 > V2 (2) V1 < V2 (3) V1 = V2 C1 PHY2049: Chapter 25 C2 21 ConcepTest When we fill the capacitor with the dielectric, what is the amount of work required to fill the capacitor? (1) W > 0 (2) W < 0 (3) W = 0 Energy lowered to U/κ C1 C2 If U is total energy in capacitor Positive work: One “pushes in” dielectric ΔU > 0 Negative work: Capacitor “sucks in” dielectric ΔU < 0 PHY2049: Chapter 25 22 Capacitors in Circuits Multi-step process 2 + 3 in series C o Combine 2 & 3 ⇒ C/2 Ceq 1 + (2+3) in parallel Combine 1 & (2 & 3) ⇒ 3C/2 2 1C 3C o PHY2049: Chapter 25 23 Example: Find qi and Vi on All Capacitors C1 is charged in position A, then S is thrown to B position Initial voltage across C1: Initial charge on C1: V0 = 12 q10 = 12 x 4 = 48μC...
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This note was uploaded on 07/31/2011 for the course PHY 2049 taught by Professor Any during the Summer '08 term at University of Florida.

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