Module-1
Ohm’s law
1
By the end of this lesson, the student will
be able to:
1-Use prefixes to convert electrical quantities.
2-State Ohm's Law and define the relationship
between current, voltage, and resistance.
3-Use Ohm's Law to solve unknown quantities
of current, resistance, or voltage.
4-Apply the power formula to calculate
the power in a circuit.
2
1- Introduction to Ohm's Law.
2-Investigations of Ohm's Law using
Edison Version 4 simulator.
3-Electrical Units and Prefixes.
4-Electrical Power.
3
It states that the current passing
through a conductor between two
points is directly proportional to
the potential difference (i.e.
voltage drop or voltage) across the
two points, and inversely
proportional to the resistance
between them, at a constant
temperature.
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Mathematical Equation is
V
I 
R
Ohm's Law Formulas
Find Current
I 
V
R
Current equals
voltage divided
by resistance
Find Voltage
Find Resistance
V
R
I
V= I x R
Voltage equals
current multiplied
by resistance
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Resistance equals
voltage divided
by current
Screen layout
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Circuit connection
9
Voltage and current measurement
10
Suppose a 10KΩ carbon resistor is connected to a
12V battery .Calculate the current flow.
I=V/R
I= 12/10000= 1.2 mA.
Suppose a solar cell provides a current of
2.5 mA to a 500 ohm load. Calculate the output
voltage of the solar cell:
V= I X R
V= 2.5mA X 500 ohm
V= 1.25 V
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Quantity
Name
Unit of Measure
Symbol Name
Voltage
U
V
Emf
Current
Resistance
Function
Symbo
l
Volt
V
Voltage is the electromotive
force or pressure which
makes current flow in a
circuit
I
Ampere
A
Current is the flow of
electrons through a
circuit
R
Ohm
Ω
Resistance is the opposition
to current flow offered by
electric devices in a
circuit
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Metric prefixes table
Number
Power of Ten
Prefix
Symbol
One billion
1,000,000,000
109
giga
G
One million
1,000,000
106
mega
M
One thousand
1,000
103
kilo
K
One
1
100
---
---
One thousandth
0.001
10-3
milli
M
One million
0.000001
10-6
micro
μ
One billionth
0.000000001
10-9
nano
n
One trillion
0.000000000001
10-12
pico
p
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Electrical power is defined as the
potential energy or voltage times the
current passing through the device.
P = VI
Where:
P = electrical power in Watt (W)
V = voltage used in Volt (V)
I = current in Amperes (A)
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Suppose an electric heater draws a current of 8A
when connected to its rated voltage of 235V. The
power rating of the heater is :
P = VI=235x8=1880W=1.88 KW
Suppose a current of 30A is being supplied to an
electric load. The total resistance of the wire used
to supply this current is 0.1 Ω. The power that lost
in the wire is:
P = I2 x R = (30)2 X 0.1 = 90 W
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