Students use potatoes to light an LED clock (or light bulb) as they learn how a battery works in a simple circuit and how chemical energy changes to electrical energy. As they learn more about electrical energy, they better understand the concepts of voltage, current and resistance.
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- Colorado: Math
- Colorado: Science
- Common Core State Standards for Mathematics: Math
- 2. Multiply or divide to solve word problems involving multiplicative comparison, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem, distinguishing multiplicative comparison from additive comparison. (Grade 4)  ...show
- 6. Use decimal notation for fractions with denominators 10 or 100. For example, rewrite 0.62 as 62/100; describe a length as 0.62 meters; locate 0.62 on a number line diagram. (Grade 4)  ...show
- 2. Use the four operations to solve word problems involving distances, intervals of time, liquid volumes, masses of objects, and money, including problems involving simple fractions or decimals, and problems that require expressing measurements given in a larger unit in terms of a smaller unit. Represent measurement quantities using diagrams such as number line diagrams that feature a measurement scale. (Grade 4)  ...show
- International Technology and Engineering Educators Association: Technology
- C. Energy comes in different forms. (Grades 3 - 5)  ...show
- Next Generation Science Standards: Science
- Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents. (Grade 4)  ...show
- Describe the flow of electrical energy through a simple circuit.
- Explain why a light bulb may take more than one battery to light up.
- Explain the role of electrical engineers in the development of electricity sources and the products that use electricity.
- 3 potatoes
- 3 copper pennies (or copper strips), one per potato
- 3 zinc nails (these are galvanized nails, available at hardware stores)
- 5 insulated wires, 15-20 cm (6-8 inches) long, with alligator clips at the ends
- 1 low-current, light emitting diode (LED) clock (or LCD clock) requiring approximately 1.5 volts (or a small LED) (available at Radio Shack or other electronics shops or websites)
- Make a Battery Worksheet, one per student
- (optional) multimeter(s) or voltmeter(s); share with the entire class or one per team; a multimeter is an instrument that measures current, voltage and resistance of a circuit; available at Radio Shack or other electronics stores or websites
|conductor:||An object that allows the transfer of electrons.|
|current:||The movement of electrons.|
|electrical energy:||Energy produced through the movement of electrons (voltage X current).|
|electrolyte:||A solution that conducts electricity.|
|energy:||The ability to do work.|
|insulator:||An object that inhibits the transfer of electrons.|
|resistance:||Objects or substances that prevent the passage of a steady electric current.|
|voltage:||Amount of energy produced.|
Before the Activity
- Gather materials and make copies of the Make a Battery Worksheet.
With the Students
- Divide the class into teams of two or three students each. Hand out the materials.
- Direct groups to carefully place the zinc nails and copper pennies into the potato. Make sure the two different metals do not touch each other in the potato (see Figure 1).
- Connect one alligator clip to the end of the penny sticking out of the potato and another alligator clip to the end of the nail sticking out of the potato (see Figure 1).
- (If you have a multimeter) Tell students that a multimeter is an instrument that measures current, voltage and resistance of a circuit, and is a tool (created by and) often used by engineers. Set the multimeter on a low "DC volts" scale for voltage and "DC milliamps" for current, so students can see the charge that one potato can produce. Expect the potato to produce just less than 1 volt. Encourage students to convert the decimal readout from the multimeter to a fraction (for example, 0.82 volts = 82/100 volts).
- Have the students figure out how many potatoes they need to light their LED clock (or clock). For example, if their potato produces a voltage of 0.8 volts, then they may need two potatoes to power a 1.5 voltage LED.
- Have students experiment to figure out how to connect two potatoes together. To connect two potatoes in series, place a penny and nail into a second potato, and connect the wire from the zinc nail in the first potato to the copper penny in the second. Then, add a third wire to the zinc nail in the second potato. Always remember to connect the copper (positive) end of the potato (battery) to the zinc (negative) end of the next potato (see Figure 2).
- Expect two potatoes in series to be able to light an LED; however, you might need three. Show students how to connect the LEDs to the potato in the correct manner, that is, the positive end of the LED to the negative end of the potato battery (zinc nail) and the negative end of the LED to the positive end of the potato battery (copper penny).
- Have students discuss how the potatoes provide the electrolyte (solution) for the chemical battery to work. Ask for suggestions of other foods we could try (for example, lemons, berries, apples).
- Ask students to complete the worksheet either individually or in pairs. After they finish, have them compare answers with a peer or another pair, giving all students time to finish.
Activity Embedded Assessment
- If a lemon produces 1 Volt of energy, how many lemons would you need to light a 2 Volt light bulb? (Answer: 2)
- If a potato produces 0.8 Volts of energy, how many potatoes would you need to light a 1.5 Volt light bulb? (Answer: 2)
- If a potato produces 0.8 Volts of energy, how many potatoes would you need to light a 3 Volt digital clock? (Answer: 4)
- If you have a lemon that produces 1 Volt of energy and an apple that produces 1 Volt of energy, can you light a 3 Volt clock? (Answer: No, you would need one more lemon or apple.)
- Have more advanced students experiment with parallel and series configurations using different numbers of potatoes.
Dictionary.com. Lexico Publishing Group, LLC. Accessed September 28, 2005. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com
Phillips, W.D. Chapter 2P: Using a Multimeter. Design Electronics (online textbook) DOCTRONICS Educational Publishing, UK. Accessed September 28, 2005. (Good design, technology and electronics resources.) http://www.doctronics.co.uk/meter.htm
Sharon D. Perez-Suarez, Jeff Lyng, Malinda Schaefer Zarske, Denise W. Carlson, Janet Yowell
© 2005 by Regents of the University of Colorado.
Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Last modified: November 25, 2015