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energy when
q
3
is at
A
and
U
B
is the potential energy when
q
3
is at
B
, then the work done
in moving the charge from
B
to
A
is
W = U
A
– U
B
= q
3
(
V
A
– V
B
) = (3.0
×
10
–6
C)(6.0
×
10
4
V + 7.8
×
10
5
V) = 2.5 J.
(d) The work done by the external agent is positive, so the energy of the threecharge
system increases.
(e) and (f) The electrostatic force is conservative, so the work is the same no matter
which path is used.
45. (a) Let
A
=
015
.
m be the length of the rectangle and
w
= 0.050 m be its width. Charge
q
1
is a distance
A
from point
A
and charge
q
2
is a distance
w
, so the electric potential at
A
is
66
92
2
12
0
4
1
5.0 10 C
2.0 10 C
(8.99 10 N m / C )
4
0.15m
0.050 m
6.0 10 V.
A
qq
V
w
ε
−−
⎛⎞
−×
×
=+
=
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This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Charge, Electric Potential

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