Notes+4+ Fall 2004

# Notes+4+ Fall 2004 - Notes 4 Fall 2004.doc Faradays law of...

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Fall 2004.doc 1 Faraday’s law of induction One way of inducing a voltage in a closed path, as we saw earlier, is to immerse the closed path in certain position dependent electric fields. This produces a non-zero path integral around the closed path that we identify as a voltage via dimensional anaylsis. Early in the history of electromagnetics it was noted experimentally that a voltage appears (is induced) in a loop of wire when a magnetic flux passing through the interior of the wire loop changes with time. This induced voltage subsequently drives a current in the wire. Faraday’s law of induction was written to reflect this phenomenon: dt d emf Φ = In this equation the emf is the voltage ( e lectro m otive f orce, in volts) that is ‘induced’ by the time- changing magnetic flux, , through the closed path. The minus sign indicates the sense of the voltage polarity as it relates to the changing flux. We’ll have more to say about that shortly. Φ It is important to note that with or without a wire present a changing magnetic flux will induce a voltage along the path defining any area through which the flux passes. However, current will only flow if the path is conducting. In this discussion we are interested in the voltage induced as a consequence of a time-varying magnetic flux through the closed path. This induced voltage (emf) can then be equated to the path integral of the electric field around the path of interest.

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## This note was uploaded on 01/20/2012 for the course EE 4460 taught by Professor Czarnecki during the Fall '10 term at LSU.

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Notes+4+ Fall 2004 - Notes 4 Fall 2004.doc Faradays law of...

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