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You can produce electricity with two metal strips and a tomato! Hear the electricity crackle using a pair of headphones. We used a ripe red tomato from a grocery store, although green tomatoes will work even better, as they are more acidic. This experiment is most impressive with metal electrodes, but many different kinds of metal will work. Try using a piece of copper wire (or a penny made before 1982), and a paper clip or galvanized nail. Although we suggest using alligator clip leads because they are easier to connect, any insulated copper or electrical wire will work well.
>>Watch our video to see the tomato battery in action!
The noise you heard was caused by the flow of electricity through the wires. This electricity was created by the reaction of the tomato pulp and metal. The zinc reacts with the acid in the tomato, and tiny particles with a negative charge (electrons) are set loose into the tomato juice. These negative electrons are pulled toward the copper electrode, which has a positive charge. (In electricity, just as in magnetism, opposites attract). Every battery has a negative side and a positive side. In the tomato battery, the copper electrode is the positive terminal, and the zinc electrode is the negative terminal. The electric current runs from negative to positive, and back around again when connected in a complete circuit.
Experiment with different kinds of electrical circuits, and test the effect it has on the noise you can hear through the headphones:
Voltage measures the force of electrons moving through a circuit, while amperage measures the amount of current (the number of electrons flowing through). In a series circuit, the voltage is doubled, but the amperage stays the same as with just one battery cell. In a parallel circuit, the amperage is doubled, but the voltage is the same as with one cell. Which kind of circuit you use depends on what balance of voltage and amperage you need.
If you want to take an accurate measure of the power in volts and amps that your tomato battery is able to produce, use a digital multimeter. You can also try powering other small electronic devices with your tomato battery! You'll need to make three or four battery cells, and connect them in a complete circuit (try both series and parallel). You can power a small light bulb or a buzzer this way. You can also experiment with other homemade batteries - use salt water, vinegar, or a potato.