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PH 112 Capacitance January 31, 2005 MJM Name _____________________ Box _______

1

Capacitance is defined as C = q/V. A capacitor can be any two conductors where we may have equal and opposite charges q, and a potential difference V between the conductors.

The unit of capacitance is the Farad (named after Michael Faraday), and 1F = 1C/V.

*Two capacitors C*

*1*

* and C*

*2*

in series have an equivalent capacitance C is given by 1/C = 1/C

1

+ 1/C

2

.

The each capacitor has the same charge q. The potential difference V is the sum of the individual potential differences: V = V

1

+ V

2

.

Two capacitors in parallel have an equivalent capacitance C = C

1

+ C

2

. The charge q on the equivalent capacitor is shared between the two: q = q

1

+ q

2

. The potential difference is the same on both capacitors and on the equivalent capacitor: V = V

1

= V

2

.

In the diagram a 6-volt battery provides a potential difference V ab

= +6v . a) Find the charge on each of the three capacitors b) Find the potential difference across each capacitance a +

+ 3

F

- 6 v 5

F

6

F q q

3

6

=

=

b - q

V

V

V

5

3

6

5

=

=

=

=

PUT UNITS ON YOUR ANSWERS

Over for one more problem.

q

6

=

V

2

=

V

3

=

V

4

=

V

6

= q

2

= q

3

= q

4

=

Find the charge on each capacitor and the potential difference across each.

2

F

+

- 12 v

6

F

3

F

4

F

2