# ch12 - Inductors Chapter 12 Inductors and Transformers A...

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1 Chapter 12 Inductors and Transformers 2 Inductors • A magnetic field in space surrounding current carrying conductor. • A common form of an inductor is a coil of wire. • Inductor’s effect is to slow the build-up and collapse of the current and oppose its changes 3 Inductors 4 Applications of Inductors • Radio tuning circuits. • Part of the ballast circuit in fluorescent lights to limit current while tuning on • In power systems, they are part of the protection circuitry used to control short- circuit currents during faults. 5 Unit: H, mH, and μ H 6 Faraday’s Experiments

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2 7 Faraday’s Experiments (cont’d) 8 Faraday’s Experiments (cont’d) 9 Faraday’s Experiments (cont’d) 10 Electromagnetic Induction • Faraday’s Law – Voltage is induced in a circuit whenever the flux linking the circuit is changing – Magnitude of voltage is proportional to rate of change of the flux linkages with respect to time 11 Electromagnetic Induction • Lenz’s Law – Polarity of the induced voltage opposes the cause producing it 12 Induced Voltage and Induction • If a constant current is applied – No voltage is induced • If current is increased – Inductor will develop a voltage with a polarity to oppose increase • If current is decreased – Voltage is formed with a polarity that opposes decrease
3 13 Induced voltage 14 Current in Inductance 15 Iron-Core Inductors • Have their flux almost entirely confined to their cores. • All flux lines pass through the windings. Flux linkage is the product of flux times number of turns. • By Faraday’s law, the induced voltage is equal to the rate of change of N Φ . Air-Core Inductors • All of the flux lines do not pass through all of the windings. • Flux is directly proportional to current. • The induced voltage will be directly proportional to the rate of change of current. 16 Iron Core e = N × the rate of change of Φ dt d N e Φ = 17 Air-core Inductor e = L × the rate of change of current dt di L e = 18 Self-Inductance • The voltage induced in a coil is proportional to the rate of change of the current.

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## This note was uploaded on 04/07/2008 for the course TECH 175 taught by Professor Yang during the Fall '07 term at Northern Illinois University.

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ch12 - Inductors Chapter 12 Inductors and Transformers A...

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