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CIRCUIT ANALYSIS
OHM’S LAW
ENGR. VIKRAM KUMAR
B.E (ELECTRONICS)
M.E (ELECTRONICS SYSTEM ENGG:)
MUET JAMSHORO
1
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.
2
battery
-
+
wiring
voltmeter
ammeter
junction
terminal
V
A
AC generator
Variable
resistance
resistance
capacitor
Variable
capacitor
3
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
4
Potential
In volts
(joules / coul)
Drop across a
resistance
Current
In amperes
(coul / second)
Current passing
Through the
resistor
Resistance
In ohms
(volts / amp)
5
volts
current
Electrons have
More Energy
Battery
Electrons get
An energy boost
current
Electrons have
Less Energy
6
volts
Resistor
Electrons have
Less Energy
Energy is lost
In the resistor
current
Electrons have
More Energy
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4.2 - Ohm’s Law
Cause
Effect 
Opposition
Every conversion of energy from one form to
another can be related to this equation.
 In electric circuits the effect we are trying to
establish is the flow of charge, or current. The
potential difference, or voltage between two
points is the cause (“pressure”), and resistance
is the opposition encountered.

Ohm’s Law
 Simple analogy: Water in a hose
Electrons in a copper wire are analogous to water in
a hose.
 Consider the pressure valve as the applied voltage
and the size of the hose as the source of resistance.
 The absence of pressure in the hose, or voltage across

the wire will result in a system without motion or
reaction.
 A small diameter hose will limit the rate at which water
will flow, just as a small diameter copper wire limits the
flow of electrons.
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Ohm’s Law
E
I
R
Where:
I = current (amperes, A)
E = voltage (volts, V)
R = resistance (ohms, )
4.3 - Plotting Ohm’s Law
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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
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(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
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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
14
All electrical circuit analysis requires the use
of two fundamental laws called
Kirchhoff’s Laws
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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 )
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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
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V2
Loop #2
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
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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.
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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
-
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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
V=-6v
A voltage
drop
resistor
V=+6v
A voltage
rise
Loop
direction
Assumed
Current flow
21
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