TE Activity: Ohm's Law I
Contributed by: K-12 Outreach Office, Worcester Polytechnic Institute
Summary |
Engineering Connection |
| Ohm's Law is the basis of all electrical systems. Electrical engineers use this equation constantly to guide the design of electrical systems. Students need a strong foundation in Ohm's law while designing circuits on their own. |
Contents
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| Grade Level: 10 (9-12) | Group Size: Not defined |
| Time Required: 3 hours |
Activity Dependency  :None |
Expendable Cost Per Group
:
US$ 3This is the cost of light bulbs, assuming that the school possess rest of the materials. |
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| Keywords: Electricity, Parallel circuits, Series circuits, Circuit components, Ohm's law, Light bulb, Light intensity | |
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Related Curriculum
:
| subject areas | Science and Technology Physics |
Pre-Req Knowledge (Return to Contents)
- Students should be introduced to electricity, current, voltage, resistance, and Ohm's Law before beginning this activity.
- The functions and structures of circuit components such as conductors, loads, and controllers should be discussed, and those existing in the circuit should be identified during the activity.
- Brief discussion of the structure of light bulbs, as well as batteries may also be included.
- Teachers may also want to ensure students are familiar with the materials they will be provided with (wires, batteries, light bulbs, multimeter (see attachment: How to Use a Multimeter), etc.), as well as the proper precautions that should be taken when working with different forms of electricity.
Learning Objectives (Return to Contents)
Application of the following:
- Ohm's Law
- Series/Parallel Circuits (ways to connect them and have an effect on V and I)
- Circuit Components
- Power
- Devices that can be used to measure voltage and current
Materials List (Return to Contents)
For each group:
- 1 6.3V light bulb
- 1 Lamp Base
- 3 AA battery holders (should include wires)
- 5 Alligator Clips
- Two 1.5 volt batteries and/or power supply
- Multimeter
Introduction/Motivation (Return to Contents)
Where would we be today without electricity? Though we may not think about it often, our lives revolve around electricity - we depend upon it for light, heat, communication, entertainment, and even healthcare. This power can not only be derived in the way we normally think about it - through power lines to our homes, schools, and places of work - but also through self-contained power sources such as batteries. Since batteries are only able to provide a set amount of voltage, (for example, a AA battery is 1.5 Volts) how do you make devices with a higher voltage requirement work without increasing the voltage of the battery?
Vocabulary/Definitions (Return to Contents)
| Ammeter: | A device that measures current flowing through the circuit. |
| Alternating Current: | Current that reverses direction at a regular rate. |
| Current: | The flow of electrons. Current is read by opening the circuit and connecting the meter in series. |
| Direct Current: | An electric current that flows in only one direction. The positive and negative terminals of a battery are always, respectively, positive and negative. The current always flows in the same direction between those two terminals. |
| Light Intensity: | The amount of light given off by a source such as a light bulb |
| Load: | A device that consumes energy or power. |
| Multimeter: | A device that measures the current, voltage and resistance. |
| Parallel Circuit: | A circuit that has two or more branches for separate currents from one voltage source. |
| Potential: | Electrical pressure, also called voltage |
| Power: | The rate at which energy is delivered to something. (quantity / time): Measured in Watts. |
| Resistance: | The opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat, light, or another form of energy. Resistance is measured in Ohms. The resistance of a device is always the same (constant). |
| Series: | Circuit that only has one path for the electrons to flow. |
| Voltmeter: | A device that measures the force with which electrons are flowing. |
| Voltage: | The force that moves electrons. Voltage is read using the meter connected in parallel. |
| Watt: | The power expended when one ampere of direct current flows through a resistance of 1 Ohm. |
Procedure (Return to Contents)
Background
Key Facts
Ohm's Law:
Ohm's Law is the relationship between voltage, current, and resistance: 
Given that the resistance (R) of a device - in this case the light bulb - is constant, if we were to change the current or voltage being provided to the device, we would have an effect on the power.
A light's intensity is proportional to the power (P) supplied to it
Power is given by Current (I) multiplied by voltage (V): 
By increasing the voltage or current supplied to a circuit, we can increase the power, and therefore increase the intensity of the light.
How can we change current or voltage (I or V)?
We can test parallel and series circuits to see how they affect the intensity of the bulb, or we can test the number of batteries connected to a circuit and the effect of this on I, V, or power.
Batteries connected in a parallel circuit increase the available current (I), but do not change the voltage (V).
Batteries connected in a series circuit cause the voltage (V) to increase, resulting in a corresponding increase in current (I).
With Students:
- Introduce the topic. Review definitions of keywords, as well as the topics mentioned in Background above.
- Group students. Depending upon the level of students, you may have them work on their own to develop an experimental procedure that tests the effect of the alignment of the batteries on voltage and current (and thus light intensity). Other students may follow the sample experimental procedure. Remind students that they will be expected to answer the questions when the experiment is over with the information they gather.
In Groups:
- Connect one 1.5 volt battery as shown in the figure to the light bulb. Measure the voltage and current of the bulb (record the data in the table) - be sure to pay attention to the light's intensity. Also draw your own schematic and label each component.
Figure 1 - Next, connect two 1.5 volt batteries in series to the light bulb (Figure 2). Again, measure the voltage and current, and remember to record your data in the table. Notice the difference in intensity of the light.
Figure 2 - Connect three 1.5 volt batteries in series (Figure 3). Once again, measure the voltage and current, and record your data.
Figure 3 - Now, connect two 1.5 volt batteries in parallel to the bulb (Figure 4) and measure the voltage and current (again record the data in your table). Is there an increase or decrease in the light's intensity?
Figure 4 - Connect three 1.5 volt batteries in parallel (Figure 5). Again, measure and record the voltage and current.
Figure 5 - Comment on the effect of number of batteries and their arrangement in the circuit on the power produced, and thus on the intensity of the light.
Attachments (Return to Contents)
- How to use a Multimeter (doc)
- How to use a Multimeter (pdf)
- Ohm's Law Data Sheet (doc)
- Ohm's Law Data Sheet (pdf)
Safety Issues (Return to Contents)
- Light bulbs will get hot.
- Alligator clips need to be used with care.
- Meters must also be used with care.
Troubleshooting Tips (Return to Contents)
- Measurements on the meters should be taken quickly to avoid damage.
Investigating Questions (Return to Contents)
- How is the brightness of the light bulb affected by the number of batteries connected in series? Explain.
- How is the brightness of the light bulb affected by the number of batteries connected in parallel? Explain.
- How is the current affected by the number of batteries connected in series? Explain.
- How is the current affected by the number of batteries connected in parallel? Explain.
- What are the advantages of connecting the batteries in parallel?
- What are the advantages of connecting the batteries in series?
- How might batteries be connected in a circuit to take advantage of both series and parallel characteristics?
Assessment (Return to Contents)
A data sheet and questions are attached and may be used as homework or a quiz/test.
References (Return to Contents)
How Batteries Work
Brain, Marshall. How Batteries Work. Retrieved February 13, 2005, from www.howstuffworks.com
Fundamentals of Physics
Halliday, D., Resnick, R., Walker, J. Fundamentals of Physics. USA: John Wiley& Sons Inc. 2005.
Electrical Engineering Principles and Application.
Hambley, A. Electrical Engineering Principles and Application. USA: Prentice Hall. 2002.
Contributors
Developed by, Ozan Baskan, Funded by, Pratt & WhitneyCopyright
© 2005 by Worcester Polytechnic Instituteincluding copyrighted works of other educational institutions; all rights reserved.
Supporting Program (Return to Contents)
K-12 Outreach Office, Worcester Polytechnic InstituteLast Modified: September 26, 2008