Did you know that you can use the juice of a lemon to power a light bulb? Actually, you can use any citrus fruit as a battery if you insert two pieces of different metal into it. The acidic juice inside the fruit chemically reacts with the two metals, and because the size of each reaction is slightly different, it sends electrons flowing. Students can construct their own lemon batteries to test a variety of parameters.
Collect a ripe lemon and roll it around on the table to release the juices, taking care not to rupture the skin. Stick a piece of two different metals into the lemon, about an inch apart and reaching the centre of the lemon but not touching. Paper clips and pennies or zinc and copper nails are common sources of metal for this project. Be careful not to poke them all the way through the lemon. Test the voltage being produced with a multimeter. Try attaching one end of a wire to each piece of metal and attaching the other end to the leads of a small LED light bulb, like a Christmas light. You can also set up multiple lemons in a series.
For a little variation on the lemon battery, try inserting various types of metal into different lemons. To make it easier to compare, keep one metal common to each lemon, only varying the other metal. For example, you could have a penny and a nickel in one, a paper clip and a penny in another, a nail and a penny in another, and two pennies together in another. When you determine which of these lemons is the most successful, try the test again keeping the other metal constant. So if you found that the paper clip and the penny created the most voltage and current, you could run a new test with a paper clip and a nickel, a paper clip and a nail, and two paper clips.
Find out what's special about the juice of a lemon by comparing its ability to act as a battery to other fruits. You could either select only citrus fruits, or you could select a wide array of fruits, including non-citrus varieties. Use the same metals to test each one, and set up the battery in the same basic way, making sure the electrodes (the metals sticking into the fruit) are equivalently spaced and equally deep. Record your findings to see which fruit created the most voltage and current.
Experiment with how big an item you can power with a lemon. Gather different sizes of light-bulbs, a small clock, a flashlight or a small motor. See what types of objects you can power with one lemon, then try putting lemons in a series and see what you can power. Use a multimeter to measure the voltage and the amperage, and see what you can deduce about why you can power some objects but not others.
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