Hands-on Activity: Potato Power
Educational Standards :
Learning Objectives (Return to Contents)
After this activity, students should be able to:
Materials List (Return to Contents)
To make a potato battery, each group needs:
For the entire class to share:
Introduction/Motivation (Return to Contents)
What is electrical energy? From where does it come? Can you think of anything that needs electrical energy to work? How about lamps, CD players or ovens? How do we get the power to run these devices? What role do electrical engineers play in improving our lives?
One place we can find electrical energy in our homes is at a wall outlet. So, how does electrical energy reach the wall outlet in our house? The energy comes from an electrical power plant, which usually makes electrical energy from burning fossil fuels, such as coal and oil. The heat energy from the burning fuel heats up water. When the water boils, it becomes steam, which flows through a pipe into a turbine (a wheel with blades). As the turbine spins from the steam, it turns a generator (a spinning magnet) that unbalances the charges in nearby atoms and produces a current of electricity. The electrical current flows through protected wires to our house.
How else can we power electrical appliances? That's right, from a battery. A battery works by providing electrons with a solution in which they can move around. Have you ever noticed that some batteries have a copper end that is positive (shown with a plus [+] sign) and another end that is negative (shown with a minus [-] sign)? Zinc is a metal that likes to give its electrons to copper. Usually, zinc just gives its electrons to copper and then the process stops. However, if you provide the electrons with a solution (called an electrolyte) to help them move to the copper, and you give the electrons a wire in which they can move from the copper back to the zinc, you can produce a circuit and a flowing path of electrical energy. (Note: Conventional current flows from positive to negative, so from the copper, through the wire, back to the zinc. The electrons actually flow negative to positive.)
A circuit is a complete path of electrical energy. This means that electrical energy or charge is produced or stored somewhere ( voltage) and has a path for the charge to flow (or current). Another part of a circuit is a resistance, such as a light bulb. Electrical engineers create circuits to help electrical energy perform work, such as lighting a room or keeping food cold. An appliance, light bulb or almost any device that uses electrical energy is a resistance. A resistance prevents or slows an electrical current or charge from moving. When electrical current flows through a source of resistance, it can be changed into light or heat or sound. Even though you cannot see it, the light bulb or appliance slows down the electrical charge.
Electrical engineers help develop the many modern products and appliances that require electrical energy. Electrical engineers also help create the technology used to generate the electrical energy in a power plant in the first place. These engineers know a lot about circuits and they continually work to find better ways to store electrical charge and generate electrical current without using nonrenewable fossil fuels such as coal and oil. These electrical engineers are very important in almost everything we do! Essentially, electrical engineers create improvements for society and help save our planet for future generations. Today, we are going to be electrical engineers and learn more about how electrical energy works in a circuit. We are also going to look at generating electrical current from the energy stored in a potato! Do you think we can light a bulb with a potato? Let's try it!
Vocabulary/Definitions (Return to Contents)
Procedure (Return to Contents)
How does a potato battery work? The copper (Cu) atoms attract electrons more than the zinc (Zn) atoms. If you place a strip of copper and a strip of zinc in contact with each other, many electrons pass from the zinc to the copper. As they concentrate on the copper, the electrons repel each other. When the force of repulsion between electrons and the force of attraction of electrons to the copper become equalized, the flow of electrons stops. Unfortunately there is no way to take advantage of this behavior to produce electricity because the flow of charges stops almost immediately. On the other hand, if you bathe the two strips in a conductive solution, and connect them externally with a wire, the reactions between the electrodes and the solution continually furnish the circuit with charges. In this way, the process that produces the electrical energy continues and becomes useful.
As a conductive solution, you can use any electrolyte, whether it is an acid, base or salt solution. Many fruits and vegetables contain juices rich in ions and are therefore good electrical conductors.
Like any battery, a potato battery has a limited life span. The electrodes undergo chemical reactions that block the flow of electricity. The electromotive force diminishes and the battery stops working. Usually, what happens is the production of hydrogen at the copper electrode and the zinc electrode acquires deposits of oxides that act as a barrier between the metal and the electrolyte. This is referred to as the electrodes being polarized. To achieve a longer life and higher voltages and current flows, it is necessary to use electrolytes better suited for the purpose. Commercial batteries, apart from their normal electrolyte, contain chemicals with an affinity for hydrogen, which combine with the hydrogen before it can polarize the electrodes.
Before the Activity
With the Students
Troubleshooting Tips (Return to Contents)
If the LED clock, light or small light bulbs do not work, check the setup of the potato battery. Perhaps the ends are not all connected from negative to positive, or perhaps there is not enough potato voltage. Check the voltage of the potato using a multimeter or voltmeter. Another possibility is having enough voltage, but not enough current to light the bulb, which is why it is recommended to use only very low-volt LED clocks or bulbs.
Lemons and oranges also work well for this activity. They work best if you first roll them on a table top, which breaks down the cells inside so more juice flows through the fruit (current).
Some people have more conduction success using copper strips instead of copper pennies.
Soaking the potatoes in Gatorade overnight can make them more conductive.
Assessment (Return to Contents)
Brainstorming: In small groups, have the students engage in open discussion. Remind them that no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Ask the students how many items they can think of that run on batteries. As a class, record their ideas on the board.
Quick Poll: Before the activity begins, ask the class a question and tally their responses on the board. Ask the students: Can we get electrical energy from a fruit or vegetable?
Activity Embedded Assessment
Worksheet / Pairs Check: Have students work individually or in pairs on the Make a Battery Worksheet. After students finish the worksheet, have them compare answers with a peer or another pair, giving all students time to finish the worksheet.
Hypothesize: Ask each group what would happen if we added more potatoes in a row to our circuit? (Answer: Adding more potatoes in a row is the same as adding batteries in a row. The voltage of each piece of potato is added up. Therefore, the voltage of our circuit would increase. On the other hand, the current of our circuit would not increase. Current is not dependent on how many potatoes but is related to the size of each potato individually.)
Problem Solving: Present the class with the following math problems and ask students to calculate how many of each vegetable or fruit are needed to light the bulb.
Diagramming: Engineers need to understand how circuits work to develop cool new technologies. Draw a picture of your potato battery. Remember to label the battery (voltage) and the resistance (light bulb). Draw an arrow for the current (from the copper end to the zinc end). List two cool products that an engineer could develop that run off a fruit battery.
Activity Extensions (Return to Contents)
At the end of the activity, before students disassemble their fruit batteries, it is fun to have the entire class connect their fruit batteries in series, making "a serious tater circle."
Have the students try the activity again using different fruits or vegetables! Many different fruits and vegetables work, including lemons, limes, apples and carrots. Have the students compare and contrast the performance of different fruits and vegetables.
Have students complete the activity again using an electrolyte solution, such as salt water or vinegar. Have the students compare and contrast the performance of different electrolyte solutions.
To add a math component, have the students use the multimeter to compare the flow of electricity for several different fruits as well as to the total amount of fruits used. Ask them to graph the results and hypothesize what is happening.
For more advanced students, have them look at parallel and series configurations using different numbers of potatoes.
Activity Scaling (Return to Contents)
References (Return to Contents)
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
ContributorsSharon D. Perez-Suarez, Jeff Lyng, Malinda Schaefer Zarske, Denise Carlson, Janet Yowell
Copyright© 2005 by Regents of the University of Colorado
The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0226322. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.
Supporting Program (Return to Contents)Integrated Teaching and Learning Program, College of Engineering, University of Colorado at Boulder
Last Modified: March 10, 2014