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solution to quiz2
1. Four capacitors are connected as shown in Fig 1. (a) Find the equivalent capacitance,
C
eq
, between
point
a
and
b
. (b) Calculate the charge
Q
on the 20
μF
capacitor if a
U
= 15
V
battery is connected
across
a
and
b
Fig 1
Answer:
C
eq
= 5
.
96
μF
;
Q
= 89
.
5
μC
hint:
The equivalent capacitance of
C
1
and
C
2
is
C
12
=
1
1
/C
1
+ 1
/C
2
so total equivalent capacitance is
C
eq
=
1
1
/C
4
+ 1
/
(
C
12
+
C
3
)
Charge on
C
4
is simply the charge on
C
eq
since it’s connected in serial with the rectangular block,
and serially connected capactors share the same amount of charge, which is also the charge of their
equivalent capacitor. Another way to see this is that the right end of
C
4
is the rightmost end of the
whole system, its left end together with the rectangular block being the “left end” of the system. Thus
Q
=
C
eq
U
2. A uniform electric ﬁeld of magnitude 250
V/m
is directed in the positive
x
direction. A 12
μC
charge
moves from the origin to the point (
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 Winter '07
 BRIANKEATING
 Capacitance, Charge

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