Erie Community College
Title III
Formula Project on Ohm’s Law
Interdisciplinary Course Materials
For Technology
Course: MT 006 (College Elementary Algebra I) or MT 013 (College Elementary Algebra)
Course Outline Topics:
· 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?
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.
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
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) 12
b) 6
c) 10
d) 25
e) Can you determine the largest value for resistance on this circuit?
4. A 12 V circuit has three resistors with resistances of 5 ohms, 6 ohms and 2 ohms. Calculate the resulting amperage and wattage.
F. 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 25% Question 2 75%
Erie Community College
Title III Grant