How a Lemon Clock Works

You’ve looked all over the house and you can’t find a battery for your alarm clock. Did you know you can make a battery from a lemon or two?

To make this battery you will need: a simple clock that runs on one AA battery, two juicy lemons, copper pennies (if you are using American pennies, choose ones from 1982 or earlier, when the copper content was changed), galvanized nails (the galvanizing process adds a coating of zinc to the nail), and small alligator clips connected by wire to close the circuits on your battery.

Take the lemons and roll them on a table or other hard surface with your hand. Rolling breaks up the fibers inside the lemon to release the juice, but don’t break the skin of the lemon. The acidic juice of the lemons is what causes the chemical reaction that creates your battery. In each lemon, insert a galvanized nail on one side. A short distance from the nail, make a small cut in the rind of the lemon, and insert a penny. The penny and the nail become electrodes for your battery. The penny is the positive electrode, the plus side of your battery, and the nail is the negative electrode.

Because the current produced by one lemon is very weak, you can double the current by using two lemons in the circuit. To connect your lemons in series, connect the penny on one lemon to the nail on the other lemon. The unconnected penny will be connected to the positive terminal on the clock, and the unconnected nail will be connected to the negative terminal on the clock. If you have connected the circuit correctly, your clock should operate.

This battery is called voltaic; it changes chemical energy into electrical energy. The lemon juice is called an electrolyte, because it breaks down the structure of the metals to release electrons. The action of the lemon juice on the two different metals creates a flow of electrons. How fast the electrons move is called voltage, and the faster the movement, the higher the voltage.

If you have a problem, you can also try using copper wire instead of the pennies. If you coil a little copper wire, you can insert the coil in the slit in the lemon, leaving a stub of wire sticking out so you can make your connection. If you have everything connected correctly, and your battery still doesn’t work, it’s possible that you will need to connect a third lemon to your circuit to increase the voltage. You can test the voltage of a single lemon battery by touching the tip of your tongue to the penny and the nail in one lemon at the same time. You should feel a little tingle on your tongue. If you have a voltmeter, you can test the voltage of your lemon batteries. To compare, one AA battery is rated for 1.5 volts.

While the lemon battery may not be practical for things that require more electricity, you will see that it does produce a small current.