Potato Battery

Electricity for kids science projects


A potato battery is the last in a series of fruit battery projects included on this site. Many versions are available, but unless you want to get fancy with the voltmeter, fruit batteries make great science projects for kids since they are both inexpensive and relatively easy to perform.

A quick look at the
lemon battery experiment will show it is the same science project, except that we use a potato here. As noted in that project, a fruit battery isn't powerful enough to light a regular bulb.

A light emitting diode, (LED), could be used to show the effect since it requires much less voltage to illuminate. However, since the room needs to be very dark to see the LED light up, I selected the voltmeter method instead. In either case, it's listed as a 5th grade science project if performed by itself. If demonstrated along with the "Turning on a Light Bulb" experiment, it could easily be used in elementary science projects from about the first grade on.

With that said, let's make a potato battery ...

Objective

We only need a potato, a couple nails and a piece of wire to make a potato battery. It's a fun science project that helps show the way things work in a battery by using everyday items we see around the house.

As in the lemon battery, the goal is to learn more about electricity, and possibly a few new science terms along the way. The project is designed to be performed on its own, but if the "Light Bulb" experiment is done at the same time, it can help connect the concept of a voltmeter reading to the familiar lighting of a flashlight bulb.





Potato Battery Project Supplies

Materials

- 1 potato
- 3 to 4 in. copper wire with the insulation removed, #12 or #18 is ok, (a copper penny works too)
- 1 steel nail, #6 or 8 is good
- 1 zinc plated nail, #6 or 8 works fine
- Small piece of sand paper
- Wire pliers or a knife to remove insulation (not shown)
- A voltmeter that can read to at least tenths of a volt

Preparation

To prepare for the potato battery project, simply gather the materials, remove insulation off the wire and lightly sand the nail ends so they will interact well with the potato.

Since the lemon and potato battery projects share the same steps, general concepts and "how it works" explanation, not all of that project info is repeated here. Major steps are listed, but please refer to the lemon battery experiment if more details are needed to conduct this lab.

Project Day

Split the class into smaller groups as materials allow. If you plan to demonstrate the light bulb project at the same time, show how the battery makes the bulb light up. Shift focus from the light to the meter by showing that the meter moves if its leads are touched to the ends of the battery as well. Then ask ... if we can make the meter move by connecting it to the potato instead of the battery, will that mean the potato is acting like a battery too? Let them know the correct answer is yes, assuming that really happens.

The nails and wire will be our test terminals for the potato battery. It does not matter which you start with, so pick any two to begin the experiment. Insert the ends about an inch deep into the potato and get them as close as you can without touching each other. (If they touch, no voltage difference will show and the meter will not move. If this happens, the battery is said to be 'shorted'. Just pick a new spot on the potato and trying again).

Put the voltmeter on a DC setting. As an optional step, test the voltmeter on an actual battery (C for ex.) if you have one handy. Although not a necessary step for the project itself, it is a good time to discuss polarity if class schedule permits. It is easy to see which terminal is the cathode (+) and which is the anode (-) on a battery because they are stamped on it. By looking at the voltmeter display and swapping the red and black leads from one end of the battery to the other, you can show how the meter displays a minus sign one way, and not the other. This information can then be used to determine which of our test terminals acts as the cathode (+) and which is the anode (-).

Potato Battery with Steel and Copper Terminals

Touch the red and black meter leads to the test terminals in the potato battery. (I tried steel and copper first). Take note of the reading, but don't get too concerned if the values each group sees are different. Readings will probably vary from setup to setup, and from trial to trial. There are a few variables we can't control with this setup, but getting a voltage reading at all ... and noting the relative values of the readings as we try different terminal materials is what is important at this point.



Potato Battery with Zinc and Steel Terminals

Shift to another terminal combination. Zinc and steel are shown to the right. Again, note the voltage. Higher? Lower?











Potato Battery with Zinc and Copper Terminals

Try the final terminal set. As in the lemon battery project, you should see why zinc and copper make good terminals.









Take the voltmeter leads off the terminals and hold them apart. Note that there is no meter reading. Touch the leads themselves together. There is still no meter reading. Try poking the ends of the leads directly into the potato without touching the test terminals. Note again that no meter deflection occurs. A meter deflection only occurs when we set up the potato battery in one of the arrangements shown above. We need two dissimilar metals as the battery terminals, and they must be inserted into the potato for the battery to work.

Share with the group that what makes a flashlight bulb light up is the same thing that makes the meter move. It is called a voltage difference.

What just happened?

For the teacher - please see the lemon battery project for a detailed discussion of what's happening. It is the same process that drives the potato battery. For more information on the theory behind the process, please see the Electricity Science Projects related to Charge section of the electricity page.

For the students - if the right metals are picked as battery terminals, a potato can in fact be turned into a battery.

To summarize, tell the group that even though the voltage in a potato battery isn't strong enough to light a flashlight bulb, it really is the same process that makes a store-bought battery work.




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