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ERIE COMMUNITY COLLEGE
TITLE III
Formula Project on Ohm’s Law
Interdisciplinary Course Materials
For Technology
Course:
Algebra)
MT 006 (College Elementary Algebra I) or MT 013 (College Elementary
Course Outline Topics:
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Perform fundamental operations (addition, subtraction, multiplication, division) with real
numbers.
Evaluate formulas, solve linear equations, linear inequalities, and ratio proportion
problems.
Demonstrate a sense of numbers by determining if a mathematical solution is
“reasonable”.
Present organized written work.
Read critically and think logically when solving application problems.
Demonstrate an understanding of order of operations to complete calculations on a
scientific calculator.
Project Title: Ohm’s Law
Project Description:
Students will use Ohm’s law to compute and solve for missing variables in circuit application
problems. Students will also compute wattage.
Author:
Lynette Meslinsky, Mathematics/Computer Science
Curriculum Expert: Robert Gannon, Automotive Technology
Semester Created:
Fall 2009
A. Essential Question
How do I use Ohm’s Law to compute voltage, amperage or resistance when two of the three
variables are known. How do I compute resulting wattage?
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Title III Grant
B. Introduction:
Simple circuit
Clarification of terms:
Ohm's Law defines the relationships between (P) power, (V) voltage, (A) current, and (R) resistance. One
ohm is the resistance value through which one volt will maintain a current of one ampere. Ohm's Law is
a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity
and electronics that it needs to be committed to memory by the serious student.
( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from
negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps. It is
indicated in the above picture by the electron flow.
( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or
pressure behind current flow through a circuit, and is measured in (V) volts. In the picture above,
voltage would be labeled by the battery.
( R ) Resistance determines how much current will flow through a component. Resistors are used to
control voltage and current levels. A very high resistance allows a small amount of current to flow. A
very low resistance allows a large amount of current to flow. Resistance is measured in ohms. The
resistor could be a single lamp (as in the above diagram) or an electrical device. It could also be a
combination of resistive devices such as several bulbs on a single circuit. Total resistance is the sum of
all resistance on a circuit.
( P ) Power is the amount of current times the voltage level at a given point measured in wattage or
watts.
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Title III Grant
There are many formulas and formula variations associated with the four definitions above. They are
depicted in the diagram below. We will only investigate two of them in this project but your teacher
may want to assign more.
C.
Things to Learn Before Starting the Project
Erie Community College
Title III Grant
You will need to know how to use your calculator to compute answers using order of operations
and exponent keys. In addition, you will need to have knowledge of how to solve an algebraic
equation written as a formula.
Formula 1: V = A x R
Formula 2: V x A = Watts
D & E. Directions & Project Assignment:
1. Look at formula 1 above.
a) Use algebra to solve the formula for A.
b) Use algebra to solve the formula for R.
c) Locate the formulas you determined in the diagram shown in the introduction.
Write the equivalent formulas here.
2. Use the most appropriate formula from Step 1 to solve each of the following problems:
a) What current would flow through a resistor of 30 ohms connected to a 9 V supply?
What is the wattage?
b) Calculate the voltage supply needed to produce a current of 15 amps when used with a
46 ohm resistor.
c) Find the size of a resistor which would limit the current to a value of .04 A when
connected to a 9 V supply. What is the wattage?
d) Calculate the voltage of a 400 ohm resistor when a current of .005 amps flows through
it. What is the wattage?
e) A resistor allows a current of .8 amps to flow when connected to a 12 V supply. What
current would flow if the same resistance was connected to a 15 V supply?
f) What is the voltage supply needed for a circuit with total resistance of 1000 ohms and .2
amps?
3. A 10 amp fuse is placed on a 110 V electric circuit. Calculate which of the resistance values listed
below will cause the fuse to blow. (i.e. amperage is  10).
a)
b)
c)
d)
e)
12
6
10
25
Can you determine the largest value for resistance on this circuit?
Erie Community College
Title III Grant
4.
F.
A 12 V circuit has three resistors with resistances of 5 ohms, 6 ohms and 2 ohms.
Calculate the resulting amperage and wattage.
Student Resources
http://phet.colorado.edu/simulations/index.php?cat=New_Sims Simulation activity for
Ohm’s law in an electrical circuit.
http://www.quia.com/jq/84444.html Ohm’s Law practice quiz
http://www.the12volt.com/ohm/page2.asp - current Ohm’s Law calculator
G.
Faculty Resources
Students will need to have developed the procedural knowledge necessary to manipulate
formulas. In addition they will need instruction in the use of a scientific calculator to execute
the mathematical operations needed to use the Ohm’s Law and Wattage formulas.
H.
Grading Rubric
All parts should be graded on Mathematical logic used through work shown (50%) as well as accuracy
(50%)
Questions 1, 3, 4
Question 2
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Title III Grant
25%
75%