Physics 1425: General Physics I - Galileo and Einstein
Physics 1425: General Physics I - Galileo and Einstein
Physics 1425: General Physics I - Galileo and Einstein
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Why the Two Surfaces Give the Same Result<br />
• The current I flowing<br />
through surface S 1 is the rate<br />
of change of charge on the<br />
top capacitor plate, I = dQ/dt.<br />
• If the plates are close, all the<br />
electric field from the top<br />
plate will point down, none<br />
will cross S 1 , so E dA<br />
/<br />
<strong>and</strong><br />
d<br />
d<br />
dQ<br />
<br />
dt dt dt<br />
<br />
E<br />
0<br />
E dA<br />
0<br />
<br />
S<br />
2<br />
S<br />
<br />
S<br />
1 2<br />
Q <br />
I<br />
0<br />
Bottom line: the rate of change of electric<br />
flux through S 2 = current through S 1 .<br />
I
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