Energy and the Environment: Division IV
Activity 1: Resistors
Integration Notes:
Students will investigate resistance and what happens to the amount of current through, and the potential difference across one resistor, when a number of resistors are connected in series. Students will then investigate what happens to the amount of current through, and the potential difference across one resistor, when a number of resistors are connected in parallel. This activity leads students to the knowledge they will need to construct their headlamp that uses LED's as a light source. (see Electricity Background, Sources of light).
Learner outcomes
Students will:
- Determine the amount of resistance provided by a resistor by examining its coloured bands.
- Determine the amount of current passing through one resistor and the potential difference across the resistor when a number of resistors are connected in series.
- Determine the amount of current passing through one resistor and the potential difference across the resistor when a number of resistors are connected in parallel.
- Use proper care and caution when handling resistors - they can get very hot when a current passes through them.
Materials:
- three radio resistors (10 Ohm to 20 Ohm)
- 6 Volt dry cell batteries
- ammeter
- voltmeter
- connecting wires
Introduction:
George Simon Ohm (1785 - 1854) was the first person to publish the results of experimentation on the resistance of wires of various sizes. Ohm constructed wires of many different lengths and thicknesses (cross-sectional areas). Today, we simply call these devices resistors because all they do is resist the flow of current. Ohm applied a potential difference (voltage) across his wire resistors and measured the current through them. He discovered that for each resistor, no matter what potential difference he applied, the resistance was the same.
Resistors are very important in circuits. (see Electricity Background, Ohm's Law) They are used to control current or potential difference in a circuit. For example, if you connect an LED to a battery (cell) you will likely destroy the LED unless you have a resistor in the circuit to control the potential difference over the LED and most importantly, the current through it.. (see Electricity Background, Sources of Light)
In this activity, students will examine the coloured bands on a variety of resistors and use the chart provided to determine their resistance. The second part of the activity explores series resistance and involves incorporating the resistors into a simple circuit and using an ammeter to determine the effect that they have on the amount of current flowing through the circuit. The third part of the activity explores parellel resistance.
Activity Instructions:
Part one:
1. Working in groups of two or three, examine a variety of resistors. Look for the colour bands as shown in this diagram.
 | The first two coloured bands (closest to one end of the resistor) are the first two digits of resistance.
The third coloured band indicates the number of zeros that follow the second digit.
|
Using the chart below, this resistor has a value of 2,700,000 Ohms (2.7 x 106 Ohms).
This value is determined by:
- First Digit (Red) = 2
- Second Digit (Violet) = 7
- Third Digit (Green) = 5 therefore, multiply by 100,000
- Total Resistance is 2,700,000 Ohms (2.7 x 106 Ohms)
2. The resistance for the resistor shown on the left can be determined as follows:
 | First Digit - (Yellow) = 4
Second Digit - (Violet) = 7
Third Digit - (Red) = multiply by 100
Total Resistance is 4,700 Ohms (4.7 x 103 W)
|
3. Draw the coloured bands that would be used to represent a resistor with a resistance of:
4. Use the colour bands to determine the resistance of the resistors available.
5. If you have a multimeter, measure the actual value of each resistor and compare it to the stated value. What is the percent error?
Note: The tolerance is the percentage error for that resistor. A resistor with a tolerance of 10 per cent means that that resistor will have an effective resistance of plus or minus 10 per cent of the value represented by the coloured bands.
- A Gold Band has a tolerance of 5%
- A Silver Band indicates a tolerance of 10%.
- No Band indicates a tolerance of 20%.
Part 2: Series Resistance
A series circuit consists of resistors connected with the voltage source in such a way that the same current travels through each resistor in turn. The Total or Equivalent Resistance (Rt) of a series circuit is the sum of all resistances of the individual resistors in a circuit. (see Electricity Background, Ohm's Law)
Rt = R1 + R2 + R3 .......
The potential difference across the voltage source is equal to the sum of the voltage drops across each resistor.
V = V1 + V2 + V3 .....
The total current flowing in the circuits is most easily found by calculating the total resistance and then dividing the voltage source potential difference (volts) by the total resistance.
I = V / R (total)
Materials:
- 2 - 1.5 volt dry cell batteries (in series out)
- 8 connecting wires
- voltmeter (0-5 volts)
- switch
- resistors 10 ohm, 30 ohm, 60 ohm (actual resistors may vary)
- ammeter (0-500 mA)
Procedure: One Resistor
1. Make a data table in your notebook with three headings across the top:
R1 (Ohms) Colour Bands; Ammeter Reading
(mA); Voltmeter Reading
(V)
| 2. Connect the circuit as shown to the right.
|  |
3. Arrange the voltmeter in parallel to the resistor.
4. Arrange the ammeter in series with the resistor.
5. Connect the cells together in series.
6. Using the colour bands, record the printed value for the resistor.
CAUTION: The resistor can get hot when a current is flowing.
7. Close the switch and record the reading on the ammeter and the voltmeter on your data chart. Do not leave the switch closed for very long.
Procedure Two Resistors in Series:
1. Create a second data chart in your notebook with four headings across the top:
Resistor 1
(Ohms); Resistor 2
(Ohms); Ammeter
(mA); Voltmeter
(V)
2. Connect a second resistor in series with the first as shown in the diagram below:
CAUTION: The resistors can get hot when a current is flowing.
3. Use the colour bands to determine the resistance (Ohms) of the second resistor.
4. Close the switch. Read and record the current in the circuit and the voltage across the two resistors.
5. Open the switch.
Procedure Three Resistors in Series:
1. Design a data chart to accommodate the third resistor.
2. Add a third resistor in series.
CAUTION: The resistors can get hot when a current is flowing.
3. Use the colour bands to determine the resistance (Ohms) of the second resistor.
4. Close the switch. Read and record the current in the circuit and the voltage across the two resistors.
5. Open the switch.
Analysis
1. For the single Resistor (R1) circuit use Ohm's Law to calculate the value of resistance obtained by experimentation.
2. Compare this value to the one obtained from the colour bands on the resistor.
3. Calculate the percent error for this resistor.
4. Use the data in the second chart to calculate the total resistance for R(1) and R(2).
5. Add the values of R(1) and R(2) obtained from the colour bands.
6. Compare the manufacturer's value for the two resistors to the value that you determined in this experiment. Calculate the percent error.
7. Use the current and voltage data in the third data chart to calculate the total resistance of the three resistors.
8. Compare this to the manufacturer's values for the three resistors and calculate the percent error.
9. How do you calculate the total resistance when a circuit consists of resistors in series?
Extension:
Change the procedure to measure the voltage drop or potential difference across the individual resistors. How is this related to the total voltage drop in a series circuit?
Part 3: Parallel Resistance
How are the current and potential difference affected as more resistors are connected in parallel?
 | Task:
Your task is to design an experimental procedure that will you to determine the current and potential difference in a circuit when three resistors are connected in parallel. |
1. Use the materials and previous activity instructions as a template for your investigation.
2. See Electricity Background, Ohms Law for additional background information on resistors in parallel.
3.Compare the current and potential difference in a circuit when the resistors are in series, to the current and potential difference in a circuit when the resistors are in parallel.
4.Include safety precautions in your procedure.
5.Have your teacher approve your experimental procedure before starting your investigation.
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Challenge: Designing a Table Lamp Incorporating LEDs
Integration Notes:
The Nepal Light Project began in 1997 when Dr. Dave Irvine-Halliday, an electrical engineer with the Faculty of Engineering at the University of Calgary, visited Nepal. Dr. Irvine-Halliday decided he would like to help the Nepalese by designing a lighting system for the rural population.
Currently, most rural homes in Nepal are illuminated by open fires, candles, kerosene wick lamps, or high-pressure camping lanterns. All of which produce waste products that reduce the quality of air in the home and are potentially dangerous.
The overall objective of the Pico Power Nepal Light Project is to design a lighting and electrical generating system that will generate sufficient electrical power to light an entire kitchen table without the pollution and fire dangers associated with the use of kerosene lamps.
For more information on the Nepal Light Project, see intro, from Phase 1.
Dr. Irvine-Halliday has challenged a group of students at the University of Calgary to work on this project. You can contact Neall Banner (banner@enel.ucalgary.ca) at the U of C for more information or for help on your own design.
Materials:
- four to six white LED lamps
- radio resistors
- other materials as required to complete the challenge
Introduction:
This challenge requires students to have knowledge of resistors and LEDs. (see Electricity Background, Ohm's Law and Sources of Light>)
Students should be encouraged to experiment with different designs and perfect their final product. One of the key features of this activity is to compare how long batteries will last when LEDs are used as a source of light rather than an equivalent luminosity using incandescent bulbs.
Teachers should emphasize development of the following skills:
- Understand the problem
- Set and/or understand the criteria
- Develop a design plan
- Carry out the plan
- Evaluate the results of the plan
- Communicate the results with others
- Produce a comprehensive final report
Activity Instructions:
1. Understand the Problem
What are the advantages and disadvantages of using LED's over incandescent bulbs? (Use a variety of print and electronic resources to locate information on LED's and how they function.)
Why do you have to use resistors if you are using LED's?
Is there an environmental benefit to using LED's rather than incandescent bulbs?
How long do rechargeable batteries last when LED's are used as the light source?
2. Set the Criteria
Develop a set of criteria that you must take into account when designing a a table lamp. The lamp must provide light to cover an area 1 metre by 1 metre.
Decide on the criteria that you will use to evaluate the design of your table lamp. e.g. coverage of area, length of battery life, appearance, environmental impact, brightness, etc. Compare your criteria with your classmates and decide on a general set of evaluation criteria.
3. Develop a Design Plan
Plan your design before you begin construction. Planning can include a clearly labelled diagram and a set of instructions. A well thought out plan can save you a great deal of time and prevent wasting resources.
Check the plan to make sure you have considered the evaluation criteria.
4. Carry out the Plan
Refer to your diagram(s) and construct your table lamp.
Test and revise your design as you progress to ensure that the final product will meet all of the evaluation criteria and be as good a product as you can make with the resources you have.
5. Evaluate
Once you have a finished product, go over the evaluation criteria once more to ensure that all have been met to the best of your ability and resources.
6. Communicate
Compare your design with those of your classmates and share your evaluations.
There may be an opportunity to communicate your results with Dr. Dave Irvine-Halliday or with other schools involved in the Everest 2000 program.
Message from Dave Irvine Halliday:
"I'd love to hear from the students with their results when I am at Everest Basecamp and to see just how they compare with those of my senior engineering students, "Team Pico." I would think that we are likely to see some quite imaginative projects and possibly something that I can apply directly to the Nepal Light Project!"
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