Background
Ohm’s law was created in 1827 by Georg Ohm
It is one of the most widely used and recognized laws
Very important basis of all electronic and electrical systems
Has remained unchanged for almost 200 years
V = Potential Difference (Volts)
I = Current (Amps)
R = Resistance (Ohms)
Ω = Universal symbol for Ohms
EI
R E IR E
RI
Ohm’s Law deals primarily with the values of:
Common terms used:
Potential Difference (Volts) - Difference in charge (positive and negative) between two separated points.
Current (Amps) – The flow of charge in a circuit, per unit of time.
Resistance (Ohms) – A measure of the opposition to current flowing through a circuit.
Series Circuit – An electric current that passes through every component of a circuit without splitting up into separate sections
Parallel Circuit – An electric current that splits up due to several components that have a point in common.
Purpose
The purpose of this presentation is to:
• Verify Ohm’s Law• Explain how it works• Demonstrate it in real circuits
I = E / R
MethodologySources Used:
• Books• Internet• Textbooks• Experimentation
Please note: The experiments performedwere not meant to make discoveries or find newconcepts, they are simply used to prove and verifyOhm’s Law
[1]
History of Georg Ohm- Was born March 16, 1789 in Erlangen
Germany
- Started career as a mathematics instructor
- Wrote an elementary book on geometry in 1812
- As a reward Georg was later sent to work at Jesuit Gymnasium of Cologne in 1817 to teach mathematics and physics
- Sophisticated equipment and instruments available to him in this school, allowed him to further his understanding of physical and mathematical principles
[2]
- His law first appeared in the book titled Die Galvanische Kette Mathematisch Bearbeite. (English translation: The Galvanic Circuit Investigated Mathematically)
- The book started with basic mathematics and then continued into his new theories of electrical properties.
- One of these properties was the proportionality of current, and voltage in a resistor, Ohm’s Law.
- He also adopted the unit of resistance, the Ohm.
Ω
Explanation of Ohm’s Law
When looking at physical systems, there is a basic concept that holds
true for almost any situation involving a change.
Ohm's law is a great example of how this relationship works.
CauseEffect
Opposition
CauseEffect
Opposition PotentialDifference
CurrentResistance
Any change to potential difference, current, or resistance has a direct
and linear effect on the other two quantities.
Consider current plotted as a function of time, with a fixed resistance.
As the voltage increases, the current should increase linearly and in a
straight line.
Using point A on the diagram above, Ohm’s Law can be used to findresistance and verify the results.
At this point, current is 8 Amps, and potential difference is 40 Volts. IfOhm’s law is rearranged to solve for resistance we should get a valueof 5 Ohms.
This simple calculation is proof of Ohm’s law, although it is important totake into consideration that this is a very basic example of therelationship.
EI
R E
RI
40
8
VoltsR
Amps 5R Ω
Application Ohm’s law is used extensively in circuit analysis to find unknown
quantities Most commonly used in the work force by electrical and electronic
engineers Used in the design process of any appliance consisting of electric
components
Some jobs that would require knowledge of Ohm’s Law:
• Car audio installation• Designing city power grids• Electronic repair jobs• Installation of home power supplies
[3]
Experimental DesignIn this experiment, 2 types of circuits were tested (Series and
Parallel)
Series configuration:
Parallel Configuration:
In these experiments, Ohm’s Law will be used to
calculate the predicted values in each circuit.
For the series circuit it will be used to predict:
• Total current• Voltage drop across each resistor
For the parallel circuit it will be used to predict:
• Current across each parallel branch
[4]
Predicted Value
Measured Value
Percent Error (%)
R Total 9 kΩ 8.85 kΩ -1.67%
I Total 2.2mA 2.23mA 1.36%
Voltage drop across R1
2.2V 2.23V 1.36%
Voltage drop across R2
10.34V 10.23V -1.06%
Voltage drop across R3
7.26V 7.34V 1.10%
Series Circuit:
Parallel Circuit
Predicted Value
Measured Value
Percent Error (%)
R total 660Ω 654Ω -0.91%
Current across R1 20mA 20.3mA 1.5%
Current across R2 4.26mA 4.34mA 1.88%
Current across R3 6.06mA 6.06mA 0%
Analysis
After completing the experiment it was found that the predicted
values were extremely close to the measured values, not exceeding
percent error of more than ±2%.
Due to the accuracy of these values, this experiment verifies that
Ohm’s Law holds true for both parallel and series circuits. No further
calculations or analysis is needed.
Possible Source of Error: fluctuating resistor values
Summary
The purpose of this presentation was to verify, explain,
And demonstrate Ohm’s Law. In the first main section
Titled “Principles of Ohm’s Law”, the law was explained
using the analogy that effect in a physical system is
equal to the cause divided by its opposition. The effect
would be the flow of charge, or current produced by the
circuit. The cause would be the applied voltage, or
potential difference introduced, and the opposition to that
flow of charge would be the total resistance of the circuit.
In the second section titled “Verification of Ohm’s Law” thelaw was verified using experimentation. The law wastested on both series and parallel circuits. Due to theVery minor discrepancy between the predicted andMeasured values, the final outcome of the experimentverified that Ohm’s Law holds true for both series andparallel circuits.
References[1] Queensland Chamber of Agricultural Societies, “Images” 2009. [Online]. Available:http://www.qcas.net.au/images/Graphics%20GIF/33_books.gif. [Accessed Dec. 5/09].
[2] BDEG, “Goerg Ohm” 2005. [Online]. Available: http://bdeg.sopron.hu/~spider/Ohm.jpg. [Accessed Dec. 5/09].
[3] XJTAG, “Images” 2006. [Online]. Available: http://www.xjtag.com/images/press/30-03-06c.jpg. [Accessed Dec.7/09].
[4] modyoursystem, “Pics” 2007. [Online]. Available: http://www.modyoursystem.com/pics/multimeter.jpg. [Accessed
Dec. 12/09].
R. L. Boylestead, “Ohm’s Law, Power and Energy” in Introductory Circuit Analysis: eleventh edition, V. Anthony, R.Davidson, and L. Dimmick, Ed., Upper Saddle River, NJ: Pearson Prentice Hall, 2007, pp. 101-105..
Wikipedia, "Ohm's Law" 2009. [Online]. Available: http://en.wikipedia.org/wiki/Ohm's_law. [Accessed Nov.24, 2009].
Wikipedia, "Georg Simon Ohm" 2009. [Online]. Available: http://en.wikipedia.org/wiki/Georg_ohm.[Accessed Nov. 27, 2009].
Physics, "Ohm's Law" 2009. [Online]. Available:http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.intro.html. [Accessed Nov. 30, 2009].
All About Circuits, "How Voltage, Current, and Resistance Relate" 2009. [Online]. Available:http://www.allaboutcircuits.com/vol_1/chpt_2/1.html. [Accessed Dec. 1, 2009].