davisnotes/elec_potenergy.html

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<title>Electricty - Electric Potential Energy - Physics 299</title>
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<center><img src="ULPhys1.gif" align="texttop" height="50"
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<h1>Electric Potential Energy<br>
</h1>
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<center><img src="celticbar.gif" height="22" width="576"><br>
<br>
<font color="#ff0000"><i>"Atomic power will make electricity too
cheap to meter</i>"</font><br>
Glenn Seaborg<br>
</center>
<img src="netbar.gif" align="middle" height="40" width="100%">&nbsp;
<br>
<ul>
<li>It is important to realize that electric potential (potential
difference - measured in Volts) is not the same thing as
electric potential energy (measured in Joules).&nbsp; We already
know how to calculate the pd dues to a system of charges,</li>
</ul>
<p align="center"><img style="width: 519px; height: 75px;"
alt="eqn2" src="elec_potential_eqn2.jpg" height="75" width="519"></p>
<blockquote>
<p align="left">or for a point charge a distance r<sub>A</sub>
from the charge<br>
</p>
<p align="center">&nbsp; <img style="width: 177px; height: 60px;"
alt="eqn6" src="elec_potential_eqn6.jpg" height="60"
width="177"><br>
</p>
</blockquote>
<ul>
<li>What about the Potential Energy, PE ?</li>
</ul>
<blockquote>
<p><img alt="elec pot energy fig1" src="elec_potenergy_fig1.gif"
align="right" height="191" width="239">Imagine two charges Q
and q , with Q at rest.&nbsp; Now gradually bring q<sub> </sub>from
infinity towards<sub> </sub>Q to point P.&nbsp; Then the work
done by an external agent in performing this task must be equal
to the negative of the work done by the electric field due to Q,<br>
</p>
<p align="center"><img alt="elec pot energy eqn1"
src="elec_potenergy_eqn1.jpg" height="54" width="314"><br>
</p>
</blockquote>
<blockquote>
<p align="left">This work is stored in the two charge system as
Potential Energy, U<sub>E</sub> ,<br>
</p>
<div align="center"><img alt="elec pot energy eqn2"
src="elec_potenergy_eqn2.jpg" height="54" width="101"><br>
<br>
<div align="left">For systems of more than 2 charges we must
consider all possible pairings to determine the total
potential energy.<br>
<br>
<img alt="exclamation" src="exclamation-icon.gif" height="30"
width="31">&nbsp; For U &gt; 0 energy must be provided to
create the system<br>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; For U &lt; 0 energy must be
provided to break up the system (initially this system is
"bound") <br>
<br>
<img alt="exclamation" src="exclamation-icon.gif" height="30"
width="31">&nbsp; Don't forget&nbsp; - Change in PE = work
needed to accomplish the change.<br>
</div>
</div>
</blockquote>
<p> <img src="netbar.gif" height="40" width="100%"> </p>
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Do you realize if it weren't for Edison we'd be watching TV by
candlelight?</span><br>
Al Boliska<br>
</p>
<img src="celticbar.gif" height="22" width="576"> <br>
&nbsp;
<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>
<br>
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