davisnotes/mag_selfind.html

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<title>Magnetism - Self Inductance - Physics 299</title>
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<h1>Self Inductance<br>
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<div class="copy-paste-block"><font color="#ff0000"><i><span
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statement that everyone believes.&nbsp; It is innocent,
unless found guilty.&nbsp; A hypothesis is a novel
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<font color="#ff0000"><i> </i><font color="#000000">Edward Teller</font></font><br>
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<li><img alt="magselfindfig1" src="mag_selfind_fig1.gif"
height="298" width="446" align="right">Consider now a single
coil/circuit/loop with N turns.&nbsp; As the current in the loop
changes the magnetic field and hence the magnetic flux through
the loop changes.&nbsp; This changing "self flux" through
Faraday's Law leads to and induced emf in the circuit,</li>
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<div align="center"><img alt="magselfindeqn1"
src="mag_selfind_eqn1.jpg" height="73" width="154"><br>
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<li>In the same manner as mutual inductance we define the self
inductance of the circuit, L, as follows</li>
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<div align="center"><img alt="magselfindeqn2"
src="mag_selfind_eqn2.jpg" height="42" width="143"><br>
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<div align="left">so that the induced emf - sometimes called
a <i><b>"back emf"</b></i> - is given by<br>
<div align="center"><img alt="magselfindeqn3"
src="mag_selfind_eqn3.jpg" height="81" width="149"><br>
<div align="left">This "back emf" always opposes the
primary emf (due to Lenz's Law), as shown in the
diagram at right.<br>
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<div align="left"><img alt="hot" src="hot.gif" height="43"
width="79"> From above, &nbsp; <img alt="magselfindeqn4"
src="mag_selfind_eqn4.jpg" height="76" width="148"
align="middle"> which can be compared to the similar
equation for capacitance&nbsp; <img alt="magselfindeqn5"
src="mag_selfind_eqn5.jpg" height="77" width="138"
align="middle"> .<br>
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<li>Calculating self inductance proceeds by the same steps
as mutual inductance - Calculate <b>B</b>, calculate
magnetic flux, then use the second equation above to
determine L.<br>
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<font color="#ff0000"><i>This girl said she recognized me from
the vegetarian club, but I'd never met herbivore. </i></font><br>
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&nbsp;<img src="celticbar.gif" height="22" width="576"> <br>
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<p><i>Dr. C. L. Davis</i> <br>
<i>Physics Department</i> <br>
<i>University of Louisville</i> <br>
<i>email</i>: <a href="mailto:c.l.davis@louisville.edu">c.l.davis@louisville.edu</a>
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