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Foundations of Technology
Ohm’s Law
Teacher Resource – Unit 4 Lesson 4
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
The BIG Idea
Big Idea:
Troubleshooting allows users to continue to
use and maintain the proper operation of a
system or product.
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Ohm’s Law
Proposed by George Ohm, and is the
relationship between Voltage, Current and
Resistance.
Voltage (V) = Current (I) X Resistance (R)
+
V
I
R
V
R
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
-
I
Ohm’s Law
Ohm’s Law is commonly expressed using
the triangle found below where:
Voltage (V) = Current (I) X Resistance (R)
Current (I) = _Voltage (V)__
Resistance (R)
Resistance (R) = _Voltage (V)_
Current (I)
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V
I
R
Voltage
Voltage (V) is the electrical force that
moves electrons through a conductor.
Voltage is electrical pressure that pushes
electrons.
V
I
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STEMCenter for Teaching and Learning™
Foundations of Technology
R
Current
Current (I) is the quantity or flow rate of
electrons moving past a point.
Current flow is also known as amperage,
or amps for short.
V
I
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STEMCenter for Teaching and Learning™
Foundations of Technology
R
Resistance
Resistance (R) is the force that reduces or
stops the flow of electrons and opposes
voltage.
V
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Using Ohm’s Law determine the missing
value for the following circuit:
+
R = ______Ώ
4.5 V
-
I
V
0.5 Amp
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
Using Ohm’s Law determine the missing
value for the following circuit:
+
R = ______Ώ
4.5 V
-
Resistance (R) = Voltage (V)
Current (I)
R = 4.5V
0.5Amp
I
V
R = 9Ώ
0.5 Amp
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
I = ______ Amp
+
R 10 Ώ
_____ V
-
Using Ohm’s Law
determine the
missing values for
the following circuit:
I
V
0.5 Amp
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
I = ______ Amp
I = 0.5 Amp
- Current will be the same
throughout the circuit
Voltage (V) = Current (I) x Resistance (R)
+
R 10 Ώ
_____ V
-
V = 0.5 Amp x 10 Ώ
V = 5V
I
0.5 Amp
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V
I
R
Resistors in Series
In a Series circuit, the current through two
or more resistors is the same, and the
circuit is connected in a series.
The total resistance of
the collection is the sum
of individual resistances.
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Resistors in Series
The total resistance of the collection is the
sum of the individual resistances.
The Equivalent Resistance
of R1, R2 and R3 when
connected in series is:
R = R1 + R2 + R3
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Practice Questions
Calculate the total resistance of the series
circuit:
5Ώ
+
9V
-
V
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
Calculate the total resistance of the series
circuit:
R = R1 + R2 + R3
R = 3 Ώ + 10 Ώ + 5 Ώ
5Ώ
+
R = 18 Ώ
9V
-
V
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
Calculate the total current of the series circuit:
(current is the same throughout a series circuit)
R(total) = 18 Ώ
5Ώ
+
9V
-
V
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
Calculate the total current of the series circuit:
(current is the same throughout a series circuit)
R(total) = 18 Ώ
5Ώ
+
Current (I) =
9V
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Voltage (V)
Resistance (R)
I = 9V
18 Ώ
I = 0.5 Amp
V
I
R
Practice Questions
Using Ohm’s Law, calculate the voltage
drop for each resistor in the series circuit:
5Ώ
+
9V
-
0.5
Amp
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V
I
R
Practice Questions
Using Ohm’s Law, calculate the voltage
drop for each resistor in the series circuit:
V=IxR
5Ώ
+
V(R1) = 0.5 Amp x 3 Ώ
V(R1) = 1.5 V
9V
-
0.5
Amp
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V(R2) = 0.5 Amp x 10 Ώ
V(R2) = 5 V
V(R3) = 0.5 Amp x 5 Ώ
V(R3) = 2.5 V
V
I
R
Practice Questions
Using Ohm’s Law, calculate the voltage
drop for each resistor in the series circuit:
5Ώ
+
9V
R1
R2
R3
Total
1.5
5
2.5
9V
Voltage
0.5
0.5
0.5
0.5 Amp
Current
3
10
5
18 Ώ
Resistance
-
0.5
Amp
10 Ώ
I
3Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Remember Current (I)
is the same across a
series circuit.
V
I
R
Resistors in Parallel
In a Parallel circuit, the voltage through
two or more resistors is the same, and the
circuit is connected in parallel.
The total resistance of the
collection is divided among
the three resistors .
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Resistors in Parallel
The total resistance of the collection is
divided among the three resistors.
The Equivalent Resistance
of R1, R2 and R3 when
connected in parallel is:
1/R = 1/R1 + 1/R2 + 1/R3
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Practice Questions
Calculate the total resistance of the
parallel circuit:
+
10 Ώ
1Ώ
V
- I
2Ώ
14.4 Amp
V
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Calculate the total resistance of the
parallel circuit:
1/R = 1/R1 + 1/R2 + 1/R3
+
10 Ώ
1Ώ
V
- I
1/R = 1/(10 Ώ) + 1/(2 Ώ) + 1/(1 Ώ)
1/R = 0.1 Ώ + 0.5 Ώ + 1 Ώ
2Ώ
14.4 Amp
1/R = 1.6 Ώ
V
R = 1/(1.6 Ώ)
R = 0.625 Ώ
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
I
R
Practice Questions
Calculate the total voltage of the parallel
circuit: (voltage is the same across a parallel circuit)
+
10 Ώ
1Ώ
R(total) = 0.625 Ώ
V
- I
2Ώ
14.4 Amp
V
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Calculate the total voltage of the parallel
circuit: (voltage is the same across a parallel circuit)
+
10 Ώ
1Ώ
V
R(total) = 0.625 Ώ
Voltage (V) = Current (I) x Resistance (R)
- I
2Ώ
14.4 Amp
V = 14.4 Amp x 0.625 Ώ
V
V = 9V
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Using Ohm’s Law, calculate the current
across each resistor in the parallel circuit:
9V
10 Ώ
+
I
1Ώ
V
2Ώ
14.4 Amp
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Using Ohm’s Law, calculate the current
across each resistor in the parallel circuit:
Current (I) =
9V
10 Ώ
+
-
Voltage (V)
Resistance (R)
1Ώ
I(R1) = 9V
10 Ώ
I
2Ώ
14.4 Amp
V
I(R1) = 0.9 Amp
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Using Ohm’s Law, calculate the current
across each resistor in the parallel circuit:
Current (I) =
9V
10 Ώ
+
-
Voltage (V)
Resistance (R)
1Ώ
I(R2) = 9V
2Ώ
I
2Ώ
14.4 Amp
V
I(R2) = 4.5 Amp
I
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
R
Practice Questions
Using Ohm’s Law, calculate the current
across each resistor in the parallel circuit:
Current (I) =
9V
10 Ώ
+
-
Voltage (V)
Resistance (R)
1Ώ
I(R3) = 9V
1Ώ
I
2Ώ
14.4 Amp
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V
I(R3) = 9 Amp
I
R
Practice Questions
Using Ohm’s Law, calculate the current
across each resistor in the parallel circuit:
10 Ώ
+
1Ώ
9V
I
Remember Voltage (V)
is the same across a
parallel circuit.
2Ώ
14.4 Amp
R1
R2
R3
Total
9
9
9
9V
Voltage
0.9
4.5
9
14.4 Amp
Current
10
2
1
0.625 Ώ
Resistance
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
V
I
R