How to make a potato battery
Credit: Maria Vamvakas and Amanda Peters
Potato Battery Activity
Batteries and their uses
Batteries are sources of portable electrical energy that produce electric current using two electrodes and a chemical substance called an electrolyte, through which electric charge can flow. Batteries can exist as dry, wet or solar cells. Wet cell batteries such as those used in cars get their power from a liquid electrolyte, dry cell batteries used in phones and laptops generate power from a slightly moist paste.
Scientists are interested in improving and creating batteries to store energy in a range of situations. Nickel-zinc batteries work well in electric vehicles while lithium ion batteries can be recharged hundred times, are mostly stable and are commonly used for portable electronics and electric vehicles such as Tesla because they tend to have a higher density and voltage capacity.
The creation of battery electric cars has generated much interest and research into batteries and technology is evolving to improve the synthesis of better performing battery electrolytes. (Refer to the website for articles and videos on this research). The desirable characteristics in creating these batteries is the ability to recharge, their reliability and most of all safety and their ability to be recycled.
Introduction: Why a Potato Battery?
A potato battery is a type of battery that is known as an electrochemical cell. The metals zinc and copper (in the nail and wire/coin) act as electrodes and react with each other, which produces chemical energy. This chemical energy is converted to electric energy through electron transfer.
The potato separates the zinc and copper, forcing the electrons trying to get from one metal to the other to travel through the potato and form a circuit. The electrons are able to flow through the potato because it acts as an electrolyte. The two metals would still react if they just touched each other without the potato, but without the barrier and electrolyte, the energy released from the reaction wouldn't form a circuit, which is what gets the power to the light bulb.
When the two wires are attached to the LED it completes this circuit, turning the light on!
Aim
To construct a cell and a battery using potatoes
In this Activity students can work in teams or pairs to create their own light bulb batteries.
Preliminary activity question
Read through the materials and method below and draw a picture of the potato battery setup using the 3 potatoes and LED below. Label the potato, wire, and light bulb parts. Draw arrows to show the direction of the current.
Materials
- 3 potatoes (fresh will work better)
- 3 galvanized nails (coated in zinc) anode black
- 3 X 5cm lengths of copper wire/small sheets of copper
- 4 Connecting wires with alligator clips attached
- 1 milliammeter
- 1 low-current, light emitting diode (LED) lightbulb (Note: longer leg is positive - connect copper to this and zinc to shorter negative end)
Method
Insert a copper nail/sheet into one end of one potato and the galvanised (zinc) nail into the other end. Note: make sure the two different metals do not touch each other in the potato. They should be 3cm apart.
Use the connecting wires to connect the copper wire to the positive terminal of the milliameter and the nail to the negative terminal. Record the electric current flowing in a Results table.
Add a second potato in series and record the electric current in your table.
Repeat step 3 by adding a third potato recording your results.
Repeat steps 2-4 but this time using the LED, recording how bright the LED shines. (Note: connect the copper electrode to the long terminal of the LED and galvanised nail to the short terminal of the LED)
Investigate the following using the milliammeter
Pushing the electrodes further into the potatoes
Increasing the distance between the copper wire and nail
Test different fruits like tomatoes, lemons and bananas
Results Table
Definitions
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: The amount of energy produced.
Discussion Questions
Does the potato battery act as a dry or wet cell? Explain.
What is the electrolyte (conducting liquid) in this potato battery? Research to find out.
Using your results describe how adding a second and third potato in series affected the electric current?
What created the electric current?
In order to make the LED glow you need a complete circuit. What components of your experimental set up enabled you to create a complete circuit? Explain
How did adding a second and third potato affect the brightness of the LED?
What would happen to the current and brightness of the LED if we connected many more potatoes? Investigate by cutting your potatoes in half and repeating the experiment.
Extension
Watch the clip “How to Make a Lemon Battery” and take notes. https://youtu.be/GhbuhT1GDpI
In an electrochemical cell one electrode needs to be more electronegative than the other. This means that the more electronegative metal has a stronger desire for electrons while the least electronegative metal gives up electrons more easily.
Referring to the video and your experiment which metal electrode had a higher electronegativity, and which had a lower electronegativity?
Which electrode acted as the anode and which acted as the cathode? Label your annotated diagram in the Preliminary activity to show the cathode and the anode.
Electricity is not coming from potato but from chemical reaction resulting from differences in electronegativities between zinc and copper. Explain how this occurs. You may want to use an annotated diagram to help you.