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A simple battery can be made by inserting a length each of zinc and copper into a lemon. Electrons flow from the zinc to the copper through the medium of the lemon juice, producing a small amount of current. The success of a lemon battery depends on choosing the largest and juiciest lemons available, using the purest samples of metal possible, and ensuring that the metal components of the battery do not come into contact with one another. The efficiency of the battery can be enhanced by gently crushing the pulp of the lemon without breaking the skin, increasing the amount of juice available to conduct the current. Lemon batteries can be best displayed by wiring several together in a circuit to provide a usable amount of power.
Choosing the best fruit for the job is an important first step in a lemon battery project. The more juice the lemons contain, the more likely they will be able to reach the maximum possible electrical output, and the longer they will continue producing current. Choosing the largest lemons available can produce more power with fewer lemons. Squeeze the lemons gently to determine how thick the skin is and select those with the thinnest skins. Avoid lemons with green or pale yellow areas of skin, as riper lemons will contain more juice.
The best electrodes are made from the purest samples of zinc and copper. A simple battery may be made using the copper in a penny and the zinc coating a galvanized nail, but the metal will be impure and relatively inefficient, resulting in lower current. Pure copper can be found in the form of household electrical wire. Typically, 18-gauge wire is the smallest size that provides the necessary stiffness to pierce the skin of the lemon. Strips of pure zinc can be purchased from scientific supply catalogs, and rolls of zinc roof flashing can be purchased from many hardware stores.
To maximize the potential of a lemon battery, roll the fruit gently on a smooth work surface to crush the pulp inside without breaking the skin. This will release more juice and improve the efficiency of the battery. Place the zinc and copper electrodes on the same side of the lemon, but far enough away from one another that there is no danger of the two metals touching and creating a short circuit. For best results, leave the electrodes in place overnight before wiring the batteries to anything, to give the juice time to penetrate any irregularities in the surfaces of the electrodes. Lightly sanding the ends of the electrodes can increase their available surface area, making them more efficient conductors for the lemon battery.
In order to produce enough electricity to light even a small LED, a lemon battery cell must be created. To do this, line up four to six lemons and connect the electrodes of each one to those of the next fruit in line, copper to copper and zinc to zinc. Connect the copper electrode of the last lemon in line to the negative terminal of a small light bulb or LED, and connect the zinc electrode to the positive terminal. Be sure and do this right before displaying the battery, as the lemons will only provide power for a limited time.