Chapter 26B - Capacitor Circuits A PowerPoint Presentation by Paul E. Tippens, Professor of Physics Southern Polytechnic State University A PowerPoint.
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Electrical circuitsElectrical circuits often contain two or often contain two or more capacitors grouped together and more capacitors grouped together and attached to an energy source, such as attached to an energy source, such as a battery.a battery.
The following symbols are often The following symbols are often used:used:
+
Capacitor
+--+ - + -
- + - + -
Ground Battery-+
Series CircuitsSeries Circuits
Capacitors or other devices Capacitors or other devices connected along a single path are connected along a single path are said to be connected in said to be connected in seriesseries. See . See circuit below:circuit below:
Series connection of
capacitors. “+ to – to + …”
Charge inside dots is
induced.
Battery
C1 C2C3
++
--
++
++
--
--
Charge on Capacitors in Charge on Capacitors in SeriesSeries
Since inside charge is only Since inside charge is only inducedinduced, , the the chargecharge on each capacitor is the on each capacitor is the samesame..
Charge is same: series connection of capacitors.
Q = Q1 = Q2 =Q3
Battery
C1 C2C3
++
--
++
++
--
--
Q1 Q2 Q3
Voltage on Capacitors in Voltage on Capacitors in SeriesSeries
Since the Since the potential differencepotential difference between between points points AA and and BB is independent of path, is independent of path, the battery voltage the battery voltage V V must equal the must equal the sum of the voltages across each sum of the voltages across each capacitor.capacitor.
Equivalent Equivalent CCe e for for capacitors capacitors in series:in series:
1
1 1n
ie iC C
1
1 1n
ie iC C
Example 1.Example 1. Find the equivalent Find the equivalent capacitance of the three capacitors capacitance of the three capacitors connected in series with a 24-V battery.connected in series with a 24-V battery.
++
--
++
++
--
--
2 F
C1 C2 C3
24 V
4 F
6 F
1
1 1n
ie iC C
1
1 1n
ie iC C
CCee for for series:series:
1 1 1 1
2 4 6eC F F F
10.500 0.250 0.167
eC
1 10.917 or
0.917ee
CC
Ce = 1.09 F
Ce = 1.09 F
Example 1 (Cont.):Example 1 (Cont.): The equivalent The equivalent circuit can be shown as follows with circuit can be shown as follows with single Csingle Ce.e.
++
--
++
++
--
--
2 F
C1 C2 C3
24 V
4 F 6 F
1.09 F
Ce
24 V
1
1 1n
ie iC C
1
1 1n
ie iC C
Ce = 1.09 F
Ce = 1.09 F
Note that the equivalent Note that the equivalent capacitance capacitance CCee for capacitors in for capacitors in seriesseries is always is always less than the leastless than the least in the circuit. (1.09 in the circuit. (1.09 F < 2 < 2 F)
1.09 F
Ce
24 V
++
--
++
++
--
--
2 F
C1 C2 C3
24 V
4 F 6 F
QC
V
Q CV
Ce = 1.09 F
Ce = 1.09 F
QQTT = C = CeeV = V = (1.09 (1.09 F)(24 F)(24 V);V);
QT= 26.2C
QT= 26.2C
For series For series circuits: circuits: QQTT = Q = Q11
= Q= Q22 = Q = Q33
Q1 = Q2 = Q3 = 26.2 C
Q1 = Q2 = Q3 = 26.2 C
Example 1 (Cont.):Example 1 (Cont.): What is the total What is the total charge and the charge on each charge and the charge on each capacitor?capacitor?
++
--
++
++
--
--
2 F
C1 C2 C3
24 V
4 F 6 F
; Q Q
C VV C
VT= 24 V
VT= 24 V
11
1
26.2 1
C3.1 V
2 F
QV
C
22
2
26.2 6
C.55 V
4 F
QV
C
33
3
26.2 4
C.37 V
6 F
QV
C
Note: VT = 13.1 V + 6.55 V + 4.37 V = 24.0 V
Note: VT = 13.1 V + 6.55 V + 4.37 V = 24.0 V
Example 1 (Cont.):Example 1 (Cont.): What is the voltage What is the voltage across each capacitor?across each capacitor?
Short Cut: Two Series Short Cut: Two Series CapacitorsCapacitors
The equivalent capacitance The equivalent capacitance CCee for for twotwo series capacitors is the series capacitors is the product divided product divided by the sumby the sum..
1 2
1 1 1;
eC C C 1 2
1 2e
C CC
C C
1 2
1 2e
C CC
C C
3 F 6 F
++
--
++
--
C1 C2
ExamplExample:e:
(3 F)(6 F)
3 F 6 FeC
Ce = 2 F
Ce = 2 F
Parallel CircuitsParallel CircuitsCapacitors which are all connected to Capacitors which are all connected to the same source of potential are said the same source of potential are said to be connected in to be connected in parallelparallel. See . See below:below:
Example 2.Example 2. Find the Find the equivalent equivalent capacitancecapacitance of the three capacitors of the three capacitors connected in connected in parallelparallel with a 24-V with a 24-V battery.battery.
CCee for for paralleparallel:l:
Ce = 12 FCe = 12 F
C2C3
C1
2 F 4 F 6 F
24 V
Q = Q1 + Q2 + Q3
VT = V1 = V2 = V3
1
n
e ii
C C
1
n
e ii
C C
CCee = (2 + 4 + 6) = (2 + 4 + 6) FF
Note that the equivalent capacitance Note that the equivalent capacitance CCee for capacitors in for capacitors in parallelparallel is always is always greater than the largestgreater than the largest in the circuit. in the circuit. (12 (12 F > 6 > 6 F)
Example 2 (Cont.)Example 2 (Cont.) Find the Find the totaltotal charge Qcharge QTT and and chargecharge across each across each capacitor.capacitor.
Example 3. Example 3. Find the equivalent Find the equivalent capacitance of the circuit drawn below.capacitance of the circuit drawn below.
C1
4 F
3 F
6 F
24 V
C2
C3
C1
4 F
2 F24 V C3,6 Ce 6 F
24 V
3,6
(3 F)(6 F)2 F
3 F 6 FC
CCee = 4 = 4 F + 2 F + 2 FF
Ce = 6 F
Ce = 6 F
Example 3 (Cont.)Example 3 (Cont.) Find the total charge Find the total charge QQTT. .
C1
4 F
3 F
6 F
24 V
C2
C3
Ce = 6 F
Ce = 6 F
Q = CVQ = CV = (6 = (6 F)(24 F)(24 V)V)
QT = 144 CQT = 144 C
C1
4 F
2 F24 V C3,6 Ce 6 F
24 V
Example 3 (Cont.)Example 3 (Cont.) Find the charge Find the charge QQ44 and voltage and voltage VV44 across the the 4across the the 4F F capacitorcapacitor
C1
4 F
3 F
6 F
24 V
C2
C3
V4 = VT = 24 V
V4 = VT = 24 V
QQ44 = = (4 (4 F)(24 F)(24 V)V)
Q4 = 96 C
Q4 = 96 C
The remainder of the charge: (144 The remainder of the charge: (144 C – C – 96 96 C) is on C) is on EACH EACH of the other capacitors. of the other capacitors. (Series)(Series)
Q3 = Q6 = 48 C
Q3 = Q6 = 48 C
This can also be found from Q = C3,6V3,6 = (2 F)(24 V)
This can also be found from Q = C3,6V3,6 = (2 F)(24 V)
Example 3 (Cont.)Example 3 (Cont.) Find the Find the voltagesvoltages across the across the 33 and and 6-6-FF capacitors capacitors
C1
4 F
3 F
6 F
24 V
C2
C3
Note: V3 + V6 = 16.0 V + 8.00 V = 24 V
Note: V3 + V6 = 16.0 V + 8.00 V = 24 V
Q3 = Q6 = 48 C
Q3 = Q6 = 48 C
3
48 C16.
3V
F0V
6
48 C8.0
6V
F0V
Use these techniques to find voltage and capacitance across each capacitor in a
circuit.
Use these techniques to find voltage and capacitance across each capacitor in a
circuit.
Summary: Series CircuitsSummary: Series Circuits
1
1 1n
ie iC C
1
1 1n
ie iC C
Q = Q1 = Q2 = Q3
Q = Q1 = Q2 = Q3
V = V1 + V2 + V3
V = V1 + V2 + V3
1 2
1 2e
C CC
C C
1 2
1 2e
C CC
C C
For two capacitors at a For two capacitors at a time:time: