DC Circuits

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Terms

DC Circuits
Ch 26 AP Physics C

Electric Circuit: A set of electrical
components connected so that they provide
one or more complete paths for charge
movement.
Emf: the energy per unit charge supplied by a
source of electric current


Circuit Analogy
That source is a charge pump that force electrons
to move in a certain direction
Any device that increse the UE of charges
circulating in a circuit is a source of emf
Symbols

These
symbols are
the common
circuit
symbols
widely used
by the
community.
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Series Circuit - Resistors
Series Circuit - Important



When 2 or more resistors are connected end to
end, they are said to be connected in series
Series Circuit
There is only one path for the current (flow of
charge, think water flow) therefore the current is the
same through each resistor
Because the + terminal of the power source is at a
nonzero electric potential and the – terminal of the
power source is at zero electric potential, the
voltages must be used up by the end of the circuit.
The voltage drop across each resistor adds up to the
total voltage available.
Series Circuit - Example
Vtotal 
V1 
I1  I 2  I 3  I total
V2 
Vtotal  V1  V2  V3
Remember t hat V  IR so...
I total Rtotal  I1 R1  I 2 R2  I 3 R3
Rtotal 
I cancels and you have :
Rtotal  R1  R2  R3
R2 
R1 
R3 
V3 
I total 
I1 
I2 
I3 
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Parallel Circuit Resistors
Parallel Circuit
Vtotal  V1  V2  V3
I total  I1  I 2  I 3
1

When two or more resistors have separate paths
for the current to get to the same point
Parallel Circuit Example
Vtotal 
Rtotal

1
1
1


R1 R2 R3
Combination Circuit
V1 
V2 
Rtotal 
R1 
R2 
R3 
V3 
I total 
I1 
I2 
I3 

A circuit that has both series and parallel
components
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How to Analyze Combos
1.
2.
3.
4.
5.
6.
Keep going
Stop at 1 equivalent resistor
Kirchhoff’s Rules


Junction Rule
(conservation of charge)
The current into a junction
must equal the current out
of the junction.
Loop Rule (conservation
of energy)
The sum of all the
voltages (drops and gains)
around any closed path
must be zero.
Kirchhoff’s Rules – Equation Form
I  0
(junction rule, valid at any junction)
V  0
(loop rule, valid for any closed loop)
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Using an Ammeter
Using a voltmeter
Using an ohmmeter
RC Circuit - Charging
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RC Circuit - Charging
RC Circuit - Charging
RC Circuit - Discharging
RC Circuit - Discharging
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RC Circuit - Discharging
RC Circuit – Time Constant

In the previous equations for charging and
discharging the capacitor two important