Activity Session
How to Make a Lemon Battery
Has your flashlight ever stopped working because the batteries were dead? It’s no fun walking around in complete darkness. Batteries are everywhere—in our toys, in our cars, in our flashlights and cell phones. But how do they work? What makes them stop working? You can learn how to make a lemon battery to learn more about these very important devices.
This video has been sourced from youtube.
Materials
Lemon or other citrus fruit (acting as the electrolyte) x4
copper wire (acting as one of the electrodes)
Wire stripper/clipper
Steel paper clip, small galvanized nail (one that is covered in zinc), or a piece of zinc (ideal) (acting as the other electrode) x4
Sandpaper (if necessary)
Voltmeter
Aim & Method
Aim:
The aim of this experiment is to create a working lemon battery and understand the concepts behind its creation.
Method:
First strip about 2 1/2 inches of plastic insulation off the copper wire. Then, clip that piece of stripped wire off the main roll.
Carefully straighten the steel paper clip. Use the wire clippers to cut it to the same length as your copper wire.
Use the sandpaper to rub out any rough spots in your wire or paperclip. You are going to be touching the wire ends to your tongue, so you want them to be smooth. If you are using the zinc covered nail or piece, scratch it lightly with the sandpaper to expose a fresh surface.
Roll the lemon gently on a table to break the cell walls and loosen up the juice inside. The sour juice is needed for the chemical reaction that you are about to start. The fact that the juice is sour should give us some hints about what kind of chemicals make up lemon juice. What do you think the sour flavour might tell us?
Carefully stick the copper wire about 1 inch into the lemon.
Connect the voltmeter to the copper wire, Is there a reading? No? why is there no reading?
Stick the paperclip, zinc covered nail or zinc strip into a spot in the lemon about 1/4 inch away from the copper wire. Make sure the wires don’t touch. The wires need to be close to each other because they will be swapping matter in the chemical reaction. If they are too far apart, the matter might lose their way.
This time touch the voltmeter to both wire ends. What do you notice?
Now repeat the creation of the lemon, copper wire and zinc nail combo and create a circuit beginning from one lemon in the circuit to 4, measure the increase or decrease in voltage using the voltmeter record your results in the table below and then create a graph labelling all appropriate components
Questions
When you touched the voltmeter to just the copper wire, you most likely would not have noticed anything unusual. When you touched the voltmeter to both metal ends, you might have noticed a slight charge being read on the voltmeter. Why do you think that is?
As more lemons were added to the circuit, what happened to the voltage? Why do you think this occurs?
If the roles of the copper wire and the zinc nail were reversed (zinc is now the cathode (positive electrode) and copper is now the anode (negative electrode) what do you think will happen to the system?
If a decrease in voltage was noticed why do you think this has occurred? What could you do to fix this issue?
What makes the use of a lemon/citrus fruit special for the creation of this battery? Why not use another fruit?
Plot a graph showing the number of lemons in circuit (along the x axis) Vs the Voltage read on the meter (along the y axis), what graph function is created? What does this tell us about voltage in lemons?
What would happen if a light bulb was placed in the circuit instead of the voltmeter? What would you expect to happen to the brightness of the bulb as more lemons are added in the circuit?
Discussion
The slight increase in charge you noticed shows that your lemon battery was generating an electric current. That means tiny electrons were moving across the surface of the voltmeter electrodes. Electrons are subatomic particles that zoom around an atom’s center and make up the part of the atom that is negatively charged.
The lemon battery you made is a type of battery called a voltaic battery. These types of batteries are made of two different metals, which act as electrodes, or places where electrons can enter or leave a battery. In your case, the electrical current entered the voltmeter, which is why there was a reading measured.
All voltaic batteries need their metals to be placed in an electrolyte. An electrolyte is a substance that can carry electrical current when dissolved in water. The tiny bit of salt in your saliva makes your saliva an electrolyte, and the sour citric acid does the same thing for lemon juice. Batteries stop working when there is not enough of the electrolyte to react with the metal or not enough metal left to react with the electrolyte.