Capacitors

1
Capacitors
2
A uniform electric field is an electric field in
which the field strength does not vary. This
gives a constant force on any charge that exists
in the field.
electric potential difference
work per unit charge force x
distance per unit charge force
per unit charge x distance
electric field strength x distance
V Ed
E V/d, with units of volts/meter
3
Capacitor
a device that stores charge
made of two conductors separated by an insulator
The amount of charge that a capacitor can store
depends on 1. area of conducting surface 2.
distance between the conductors 3. type of
insulating material
link
4
Capacitance
the ratio of charge to potential difference
Q CV
C Q/V
The SI unit of capacitance is the Farad, F, named
in honor of Michael Faraday.
One Farad of capacitance means that one Coulomb
of charge may be stored in the capacitor for each
Volt of potential difference applied.
5
Capacitor Circuits
Series
1. reciprocal of the total capacitance is the
sum of the reciprocals of the separate
capacitors
1/CT 1/C1 1/C2 1/C3 ...
2. charge is the same on each capacitor
QT Q1 Q2 Q3 ...
3. total potential difference is the sum of each
VT V1 V2 V3 ...
In other words, in a series circuit, capacitance
adds as reciprocals, charge stays the same, and
voltage adds.
6
C, mF
V, V
Q, mC
E 12 V
C1
12
C1
C3
C2
10
C3
15
CT
C2
VT
QT
7
C, mF
V, V
Q, mC
E 12 V
C1
48
4.0
12
C1
C3
C2
48
10
4.8
48
C3
15
3.2
CT 4.0 mF
C2
VT 12 V
QT 48 mC
8
Parallel
1. total capacitance is the sum of each
separate capacitor
CT C1 C2 C3 ...
2. total charge is the sum of the charges on
each separate capacitor
QT Q1 Q2 Q3 ...
3. potential difference is the same across
each capacitor
VT V1 V2 V3 ...
In other words, in a parallel circuit,
capacitance and charge add, but voltage stays
the same.
9
C, mF
V, V
Q, mC
E 12 V
C1
8
C2
10
C1
C3
4
C2
CT
C3
VT
QT
10
C, mF
V, V
Q, mC
E 12 V
C1
8
12
96
C2
12
10
120
C1
C3
4
12
48
C2
CT 22 mF
C3
VT 12 V
QT 264 mC
11
Capacitors are often used in conjunction with
resistors in simple circuits that are called RC
Circuits. Click here and here to view
computer simulations of this type circuit.
Explore this link to learn more about capacitors.