A battery produces electricity by a chemical reaction between two different metals: copper and zinc. When placed in an acidic solution, an electric current is generated between the metals. A common lemon can serve as the acid. A copper penny and zinc galvanized nail will work as the metals. When the nail and the penny are inserted into the lemon, they form a battery. When a number of these lemon batteries are chained together, they can be used to light an LED.
Insert a galvanized nail in the end of each of the four lemons. Make an incision in the opposite end of each lemon and insert a penny halfway into each incision.
Connect the galvanized nail in one lemon to the penny in another lemon with an alligator clip lead. Connect the rest of the lemons in the same manner to chain the lemons together.
Connect an alligator clip lead to the penny in the first lemon. Connect the last alligator clip lead to the galvanized nail in the last lemon.
Turn the volt meter on. Connect the alligator clip lead from the galvanized nail in the first lemon to the black lead on the volt meter. Connect the alligator clip lead from the penny in the last lemon to the red lead on the volt meter. Check the volt meter reading to ensure that the lemons are putting out around 3.5 volts.
Disconnect the volt meter. Connect the alligator clip lead from the galvanized nail in the first lemon to the negative wire on the LED. Connect the alligator clip lead from the penny in the last lemon to the positive wire on the LED. The LED will light, dimly.