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Unformatted text preview: Chapter 30 – Inductance Mutual Inductance SelfInductance and Inductors MagneticField Energy The RL Circuit The LC Circuit The LRC Series Circuit 1. Mutual Inductance A changing current in coil 1 causes B and a changing magnetic flux through coil 2 that induces emf in coil 2. dt d N B 2 2 2 Φ = ε 1 21 2 2 i M N B = Φ 1 2 2 21 1 21 2 i N M dt di M B Φ = → = ε dt di M dt d N B 1 21 2 2 = Φ Magnetic flux through coil 2: Mutual inductance of two coils: M 21 M 21 is a constant that depends on geometry of the coils = M 12 . dt di M dt di M 2 1 1 2 = = ε ε 2 1 1 1 2 2 i N i N M B B Φ = Φ = If a magnetic material is present, M 21 will depend on magnetic properties. If relative permeability (K m ) is not constant (M not proportional to B) b Φ B2 not proportional to i 1 (exception). Ex. 30.1 Mutual inductance: emf opposes the flux change Only a timevarying current induces an emf. Units of inductance: 1 Henry = 1 Weber/A = 1 V s/A = 1 J/A 2 2. Self Inductance and Inductors i N L B Φ = dt di L dt d N B = Φ dt di L = ε When a current is present in a circuit, it sets up B that causes a magnetic flux that changes when the current changes b emf is induced. Lenz’s law : a selfinduced emf opposes the change in current that caused it b Induced emf makes difficult variations in current. Selfinductance Selfinduced emf dt di L l d E n = ∫ a a Inductors as Circuit Elements Inductors oppose variations in the current through a circuit. In DCcircuit, L helps to maintain a steady current (despite fluctuations in applied emf). In AC circuit, L helps to suppress fast variations in current. Reminder of Kirchhoff’s loop rule: the sum of potential differences around any closed loop is zero because E produced by charges distributed around circuit is conservative E c ....
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This note was uploaded on 07/30/2011 for the course PHY 2049 taught by Professor Saha during the Spring '08 term at University of Central Florida.
 Spring '08
 SAHA
 Physics, Current, Inductance, Energy

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