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# ch2223_print - Inductance and Alternating Current Circuits...

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Inductance and Alternating Current Circuits 1 – Self-inductance Consider a circuit consisting of a switch, a resistor, and an emf. S R I B ε When the switch is closed, the current does not change immediately from zero to its maximum value ε/R but only increases gradually. As the current increases with time, so does the magnetic flux through the loop (which is due to the current in the loop). Dr.D.Wackeroth Spring 2005 PHY102A Inductance and Alternating Current Circuits Lenz’s law the induced emf in the loop is opposite to the direction of the current. The opposing emf results in only a gradual increase of the current. This effect, i.e. that a changing current induces an emf in the same circuit, is called self-inductance . For the same reason, if the switch is opened, the current only gradually decreases to zero. Faraday’s law: ε = - N ∆Φ The magnetic flux is proportional to the magnetic field, which is pro- portional to the current in the circuit. Dr.D.Wackeroth Spring 2005 PHY102A

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Inductance and Alternating Current Circuits Thus, the self-induced emf is proportional to the time rate of change of the current: ε = - L I t (1) L is called the inductance of the device. The SI unit of inductance is the henry (H) : 1 H = 1 V · s/A Relation between self-inductance and magnetic flux: N ∆Φ = L L = N Φ I (2) The emf induced by an inductor prevents a battery from establishing a current in a circuit instantaneously. The battery has to do work to produce a current. The energy stored by an inductor is Energy = 1 2 LI 2 (3) Dr.D.Wackeroth Spring 2005 PHY102A Inductance and Alternating Current Circuits 2 – Mutual Inductance The effect that a changing current in one circuit (=primary circuit) induces an emf in another circuit (=secondary circuit) is called mutual inductance
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## This note was uploaded on 02/12/2012 for the course PHYSICS 104 taught by Professor Staff during the Fall '10 term at Rutgers.

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ch2223_print - Inductance and Alternating Current Circuits...

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