Imagine telling your friends about your latest science project: using a battery to make a light turn on. You might get some blank stares. sounds a little boring and basic, right? Now tell them you will do it with a potato! Yes, you can actually turn fruits and vegetables into electric power sources! Batteries power many things around you, including cell phones, wireless video game controllers, and smoke detectors. In this science project, you will learn about the basics of battery science and use potatoes to make a simple battery to power a small light and a buzzer.
Make batteries by pushing zinc and copper electrodes into potatoes, then investigate how to combine them in series and in parallel to power a buzzer and an LED.
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Last edit date: 2015-02-23
There are many types of batteries, ranging from tiny watch and hearing aid batteries that are just a few millimeters wide, to the normal AA batteries you use in many household electronic devices, to the large batteries you find under the hood of a car. Did you know that you can also use a potato as a battery? That might sound weird, but believe it or not, you can actually use a potato as an electrical battery to power small devices. To understand how, first you will need to learn a little more about batteries.
Batteries are containers that store energy, which can be used to make electricity. This method of storing energy allows us to make portable electronic devices (imagine what a pain it would be if everything had to be plugged into a wall outlet to work!). There are many different types of batteries, but they all depend on some sort of chemical reaction to generate electricity. The chemical reaction typically occurs between two pieces of metal, called electrodes. and a liquid or paste, called an electrolyte. It turns out that the moisture inside a potato works pretty well as an electrolyte, so you just need to add some metal electrodes to a potato, and you have a battery! Note: You do not need to understand the details of the chemical reaction in order to do this science project. If you want to learn more, do additional research about "battery chemistry."
Next, you need to understand some basic concepts about electricity. The flow of electricity is called an electrical current. which is measured in a unit called amperes (also called amps for short). The symbol for amperes is A. A common analogy used for electrical current is to imagine water flowing through a pipe. The faster the water flows, the more "current" there is.
Electrical current cannot just flow on its own; it needs something to "push" it. Voltage (also referred to as electric potential ) is what pushes electrical current through wires. Voltage is measured in volts. and the symbol for volts is V. Using the water analogy, voltage is like the pressure that pushes the water. Higher pressure will push the water faster, generating more current.
Finally, electrical resistance resists the flow of current, making it harder for electricity to flow. Resistance is measured in ohms. and the symbol for ohms is Ω. As resistance increases, it takes more voltage to push the same amount of current. Think of resistance like a pipe that is clogged with debris; the more clogged the pipe is, the harder it will be to push water through.
An electrical circuit is like a path through which the electricity can flow. Circuits can be very complex, with millions and millions of components (like the ones inside your computer), or very simple, with just two components, like a battery and a lightbulb. This science project will focus on simple battery-powered circuits. In general, a battery supplies a certain voltage to a circuit. How much current is drawn out of the battery depends on the load. or what the battery is connected to.
Batteries have positive and negative terminals. In order for electricity to flow in a battery-powered circuit, there must be a complete path from the positive terminal to the negative terminal. This is called a closed circuit. If the path is broken, electricity cannot flow. This is called an open circuit. Figure 1 shows closed and open circuits in a simple circuit with a lightbulb attached to a battery.
Figure 1. In a closed circuit (left), there is a complete path from the positive to the negative terminal of the battery, so electrical current can flow, and the lightbulb will light up (the yellow arrows represent electrical current). In an open circuit (right), one of the wires is disconnected, so the path is broken, which prevents electricity from flowing, so the
lightbulb does not light up. Note that most batteries have a plus (+) sign printed on one end, but do not have the minus sign printed on them.
Electricity likes to take the "path of least resistance" (just like water). The lightbulb in Figure 1 has a much higher resistance than the wires; the wires by themselves have a very low resistance. So, if possible, the electricity would prefer to just flow through wires, and avoid the lightbulb altogether (remember the "clogged pipe" analogy; water would rather flow through an empty pipe than through a clogged pipe). So, if a wire is put in the wrong place, this could create a short circuit. as shown in Figure 2. A short circuit can be very dangerous; it can result in a large amount of current being drawn from the battery, which can result in the battery overheating and even exploding! Luckily, vegetable batteries only supply a very small amount of current, so they are safer to work with.
Figure 2. A short circuit occurs when the battery's positive and negative terminals are connected directly to each other with electrical wires. In this case, almost all of the current (represented by yellow arrows) flows through the wire instead of through the lightbulb. Electrical wires have very low resistance, so this allows a large amount of current to flow and can be dangerous.
What about circuits that have more than just a single battery? You have probably used many devices that require two or more batteries, like toys or remote controls. Multiple batteries can be connected two different ways: in series or in parallel. When multiple batteries are connected in series. the positive terminal of one battery is connected to the negative terminal of the next battery (and this repeats if there are more than two batteries). When batteries are connected in parallel. all of the positive battery terminals are connected together, and all of the negative battery terminals are connected together. These two configurations are shown in Figure 3.
Figure 3. When batteries are connected in series (top), the positive terminal of one battery is connected to the negative terminal of the next. When they are connected in parallel (bottom), all the positive terminals are connected, and all the negative terminals are connected.
So why would you choose one method over the other? The amount of voltage and current that can be supplied by multiple batteries changes depending on whether you connect them in series or in parallel, and certain electronic devices might require a certain amount of voltage or current. For example, have you ever noticed how a small device like a TV remote or computer mouse might only require two AAA batteries, but a larger toy or flashlight might require four or more AA batteries? This is because each device has different electrical requirements to operate properly.
You can measure how much voltage or current a certain number of batteries can provide by determining the batteries' open-circuit voltage and short-circuit current. A battery's open-circuit voltage is the voltage across a battery's terminals when it is not attached to anything. This is the highest voltage that a battery can supply (the voltage will drop slightly when the battery is attached to a load). The short-circuit current is the current when the battery's terminals are shorted together. This is the highest current the battery can supply (the current will also drop when the battery is attached to a load). How exactly do the voltage and current change when your batteries (potatoes) are configured in series or in parallel? That is what you will investigate as you do this electronics science project!
For circuits with three or more batteries, it is possible to do combinations of series and parallel connections. This introductory science project will only discuss purely parallel or purely series circuits.
That was quite a lengthy introduction to electronics! Do not worry if the introduction seemed like too much information to remember. The Procedure section of this science project will carefully walk you through connecting potato batteries in series and in parallel (you can also read more about electricity in the Electricity, Magnetism, & Electromagnetism Tutorial ). You will use a multimeter to measure their voltage and current, and check to see if your potato batteries can power a small light, called a light-emitting diode (LED), or a buzzer. Be sure to review the terms, questions, and references listed below before moving on to the Procedure tab.
Terms and Concepts
- Chemical reaction
- Electrical current
- Closed circuit
- Open circuit
- Series circuit
- Parallel circuit
- Open-circuit voltage
- Short-circuit current