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W. Sautter 2007
AMPS
volts
Ammeters measure
current in amperes
and are always
wired in series in
the circuit.
Voltmeters measure
potential in volts
and are always
wired in parallel
in the circuit.
battery
-
+
wiring
voltmeter
ammeter
junction
terminal
V
A
AC generator
Variable
resistance
resistance
capacitor
Variable
capacitor
ELECTRONS
INTO
LOAD
LOAD
(RESISTANCE)
[ENERGY OUT]
ELECTRONS
OUT OF LOAD
CONDUCTOR
CONDUCTOR
ELECTRONS
OUT OF SOURCE
HIGHER ENERGY ELECTRONS
ELECTRON
PUMP
(SOURCE VOLTAGE)
[ENERGY IN]
ELECTRONS
BACK TO
SOURCE
LOWER ENERGY ELECTRONS
Potential
In volts
(joules / coul)
Current
In amperes
(coul / second)
Drop across a
resistance
Current passing
Through the
resistor
Resistance
In ohms
(volts / amp)
volts
current
Electrons have
More Energy
Battery
Electrons get
An energy boost
current
Electrons have
Less Energy
volts
Resistor
Electrons have
Less Energy
Energy is lost
In the resistor
current
Electrons have
More Energy
There are three generally types of electrical circuits:
(1) Series circuits in which the current created by the voltage
source passes through each circuit component in succession.
R2
A2
A1
R3
R1
Arrows show
Current path
Through each
component
(2) Parallel circuits in which the current created by the voltage
source branches with some passing through one component and
while the rest of the current passes through other components.
R1
A1
R2
A2
R3
A3
Arrows show
Current path
Through each
component
Junction or
Branching points
R4
A4
P
A
R
A
L
L
E
L
R1
A1
R2
A2
R3
A3
(3) Series Parallel circuits
or combination circuits
which contain series
segments and parallel
segments.
Arrows show
Current path
Through each
component
R4
A4
SERIES
All electrical circuit analysis requires the use
of two fundamental laws called
Kirchhoff’s Laws
FIRST LAW
All current entering a junction point must
equal all current leaving that junction point
Current
Leaving ( I3 )
Current
Leaving ( I2 )
Junction
point
I1 = I2 + I3
Current
Entering ( I1 )
SECOND LAW
Around any complete loop, the sum of the
voltage rises must equal the sum of voltage drops
Resistance 1
(voltage drop 1)
Resistance 2
(voltage drop 2)
Resistance 3
(voltage drop 3)
Current flow
Complete loop
+
Battery
(voltage rise)
-
V(Battery) = V1 + V2 + V3
Loop #2
V2
R2
A2
Loop #3
Complete current
Paths in a circuit
V1
R1
A1
Loop #1
EMF
+
At
Battery
Kirchhoff’s Laws
Around a loop
 V rises =  V drops
A loop is a completed
Path for current flow
When using Kirchhoff’s laws we apply the principles
of conventional current flow.
When current leaves the positive (+) terminal of
a voltage source and enters the negative (-) terminal
a voltage rise occurs across the source. If the current
enters the positive and exits the negative a of a voltage
source a voltage drop occurs across the source.
When tracing a current loop, if the assumed direction
of the current and the loop direction are the same,
a voltage drop occurs across a resistance.
If the assumed direction of the current and the
loop direction are opposite, a voltage rise occurs
across the the resistance.
When using Kirchhoff’s laws we apply the principles
of conventional current flow.
When current leaves the positive (+) terminal of
a voltage source and enters the negative (-) terminal
a voltage rise occurs across the source.
If the current enters the positive and exits the negative
a of a voltage source a voltage drop occurs across
the source.
V=-6v
Current
flow
+
V=+6v
Battery
( 6 volts)
Current
flow
-
When tracing a current loop, if the assumed direction
of the current and the loop direction are the same,
a voltage drop occurs across a resistance.
If the assumed direction of the current and the
loop direction are opposite, a voltage rise occurs
across the the resistance.
Loop
direction
Assumed
Current flow
resistor
V=+6v
A voltage
rise
Loop
direction
Assumed
Current flow
V=-6v
A voltage
drop
In a series circuit:
(1) The total resistance of the circuit is the sum of
the resistance values in the circuit.
Series Resistance
Rt = R1 + R2 + ….
(2) The sum of all voltage drops across the resistors
in the circuit equals the voltage rise of the source.
EMF = V1 + V2 + V3 + Vi
The through each resistance is the same.
I TOTAL = I1 = I2 = I3 = Ii
Voltmeters
In parallel
Ammeters
In series
Series Resistance
Rt = R1 + R2 + ….
V2
R2
EMF = V1 + V2 + V3 + Vi
A2
A1
R3
V1
R1
EMF
Ri
R = Resistance
In ohms
V3
Ammeters read
The same everywhere
In the circuit
A1 = A2
In a parallel circuit:
(1) The reciprocal of the total resistance of the circuit is the sum
of the reciprocals of the resistance values in the circuit.
Parallel Resistance
1/Rt = 1/R1 + 1/R2 ….
(2) The sum of the voltage drops across the resistors in a branch
of the circuit equals the voltage rise of the source.
V source= V1 = V2 = V3 = Vi
(3) All current entering a junction = all current
leaving the junction
I TOTAL = I1 + I2 + I3 + Ii
Voltmeters
In parallel
V1
R1
A1
Ammeters
In series
V2
R2
Junction
points
A2
Parallel Resistance
1/Rt = 1/R1 + 1/R2 ….
V3
R3
A3
EMF
A4
R = Resistance
In ohms
Battery
Kirchhoff’s Laws
(1) All current entering
A junction = all current
Leaving the junction
(2) Around a loop
 V rises =  V drops
V1
P
A
R
A
L
L
E
L
R1
A1
V2
R2
A2
V3
R3
V4
Parallel Resistance
1/Rt = 1/R1 + 1/R2 ….
Series Resistance
Rt = R1 + R2 + ….
R4
A3
EMF
Ri
SERIES
A4
Kirchhoff’s Laws
(1) All current entering
A junction = all current
Leaving the junction
(2) Around a loop
 V rises =  V drops
Integrated
circuits
resistors
capacitors