R - Galileo and Einstein
R - Galileo and Einstein
R - Galileo and Einstein
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Potential Energy of Dipole in Electric Field:<br />
<br />
Torque Approach<br />
2 QE / 2 sin pE sin ,<br />
• d +Q<br />
pE.<br />
• A torque does work<br />
p<br />
dW d<br />
on turning through angle d ,<br />
so the total work on going<br />
from 90 to is:<br />
U<br />
<br />
0<br />
<br />
<br />
<br />
<br />
90<br />
90<br />
0<br />
0 0<br />
W d pE sin d pE cos<br />
p E<br />
p<br />
E.<br />
-Q<br />
<br />
Why is this negative? Remember when an object<br />
falls, the gravitational force does positive work on<br />
it, <strong>and</strong> it’s losing that amount of potential energy.
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