ch25_p28 - 28(a The potential difference across C1(the same...

28. (a) The potential difference across C
1
(the same as across C
2
) is given by
( )( )
3
1 2
1 2 3
15.0 F 100V
50.0V.
10.0 F+5.00 F+15.0 F
C V
V V
C C C
µ
µ µ µ
= = = =
+ +
Also, V
3
= V – V
1
= V – V
2
= 100 V – 50.0 V = 50.0 V. Thus,
( )( )
( )( )
4
1 1 1
4
2 2 2
4 4 4
3 1 2
10.0 F 50.0V 5.00 10 C
5.00 F 50.0V 2.50 10 C
5.00 10 C 2.50 10 C=7.50 10 C.
q CV
q C V
q q q
µ
µ
−
−
− − −
= = = ×
= = = ×
= + = × + × ×
(b) The potential difference V
3
was found in the course of solving for the charges in part
(a). Its value is V
3
= 50.0 V.
(c) The energy stored in C
3
is
( )( )
2
2 2
3 3 3
1 1
15.0 F 50.0V 1.88 10