How to Light Up a Light Bulb With Citrus Fruit

Diagram of a fruit battery.

You can use citrus fruit to light up a light bulb by making a fruit battery. Fruit batteries are an ideal science fair project for elementary and middle school students. They're fun, safe and inexpensive.
Here's the simple version of how fruit batteries work. When you put two unlike metals in a liquid, they generate electricity. The metals are called the electrodes. The liquid is called the electrolyte. How much electricity is generated depends on how different the metals are on the atomic level. Copper, for instance, has 29 electrons in each of its atoms. Zinc has 30. Gold has a whopping 79. A lemon or grapefruit works great as a self-contained package of fluid, and the acidity of the juice conducts electricity better than an alkaline or neutral liquid. Attach the light bulb's wires to the electrodes, and you have a fun demonstration of how electricity works.

Things You'll Need

• Large lemon
• Empty egg carton
• 2-inch copper nail
• 2-inch galvanized nail
• 6-volt miniature lamp with leads
• Wire stripper
• 2 alligator clips
• Micro voltmeter (optional)

Instructions

1. Roll the lemon between your palm and the kitchen counter-top until you feel it soften. Don't break the skin or cut it. Rolling the lemon will release the juice inside the peel, and help the electricity flow between the electrodes.

2. 

   Place the rolled lemon in a compartment in the egg carton to keep it from rolling away.

3. Push the nails half-way into the fruit about 2 inches apart. Don't let them touch, and don't push them in so far that they pierce the skin on the opposite side.

4. 

   Check the leads on the bulb. If the wire is insulated to the end of each lead, strip off 1 inch of insulation with the wire stripper.

5. Wrap one end of the bare wire lead around the copper nail; wrap the other around the galvanized nail.

6. 

   Apply the alligator clips to the wrapped wires to keep them in place around the nails.

Tips & Warnings

• This principle is why a little piece of foil can make a filling in your tooth hurt. Your saliva helps the aluminum in the foil and the metal in your filling create an electrical charge. You can attach a micro voltmeter to your lemon battery and track the voltage. You can experiment with different kinds of fruit and vegetables to see which produce the most electricity. Try using different kinds of nails or other metal objects. Supplies for this project can be purchased at electrical supply and home improvement stores. Also consider shopping at military surplus stores.

• Use caution when working with electricity.

References

• Science Adventure: Fruit Battery

Resources

• eHow: Make a battery out of fruit juice
• Radio Shack