الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Capacitors and capacitance
Example 6.7
Consider the circuit shown in figure 6.10 where
C 1 =6µF, C 2 =3µF, and V=20V. C 1 is first charged
by closing switch S 1 . S 1 is then opened, and the
charged capacitor C 1 is connected to the
uncharged capacitor C 2 by closing the switch S 2 .
Calculate the initial charge acquired by C 1 and
the final charge on each of the two capacitors.
Solution
When S 1 is closed, the charge on C 1 will be
Q 1 =C 1 V 1 =6µF 20V=120µC
Figure 6.10
When S 1 is opened and S 2 is closed, the total charge will remain constant
and be distributed among the two capacitors,
Q 1 =120µC-Q 2
The potential across the two capacitors will be equal,
Q
C
1
V = =
1
Q
C
120µ
F − Q 2
Q2
=
6µ
F 3µ
F
Therefore,
Q 2 = 40µC
2
2
Q 1 =120µC-40µC=80µC
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