project 3

HOW TO MAKE A LEMON-POWERED CLOCK

A pair of lemons and a quick trip to the hardware store is all you need to convert natural chemical energy into electrical power.
Alessandro Volta invented the battery in Italy, in 1800, combining zinc, copper, and an acid to create energy. A common lemon can provide the acid (you can also use a potato if there's no lemon around), and you can rig one to run your own digital clock.

What you need:

—A battery operated digital clock without a plug. It can use two AA batteries, or a round battery. Depending on the connections, you have to rig the wires in different ways, but that's where the fun starts.
—Two fairly large galvanized nails. Nails are measured in length (in inches) and in diameter (with designations of 3d, 6d, 8d, 10d, and the like). We used a 16d, 3 1/2 inches--a solid nail. Galvanized nails are a must and we'll explain why below.
—Copper wire. Uncoated wire is easier. If your wire comes with a coating, use a wire stripper to remove an inch or two of the covering.
—Three electrician's clips.
—Two lemons, or one very large lemon cut in half.

What you do:

In five simple steps, here is how you run a digital clock on a lemon.
STEP ONE: Place the lemons on a plate, or any flat surface that can serve as the base for the clock. Push one nail into each lemon and then, as far away from the nails as possible, also push in a strand of copper wire. Label your lemons one and two. What you're going to do now is create a closed circuit, so energy can flow from the lemon into the clock and back again.
STEP TWO: Open up the clock's battery compartment. Depending on your clock, there are two AA batteries, or a single battery that looks like a button. Remove the battery (you'll be replacing its energy, believe it or not, with the lemon-nail-and-copper concoction you've just created). Notice that the positive and negative points are marked as such.
STEP THREE: On lemon number one, use the electrician's clip to connect the copper wire to the positive point in the clock. This may be a challenge; in some cases it's easier said than done.
If you can't connect your wire to the positive point in the batter compartment, you'll need to remove the clock's plastic backing and open up the clock. An adult should help with this, and remember, once you take the clock apart it may not go back together. Inside, you'll see that the positive and negative points are connected to wires on the inside of the clock. You can remove the wires from the back of the battery compartment, and then use them to make your connections. If you have a two-AA-battery clock, and inside you find two positive wires, make sure you connect your copper wire with both. Once you've figured this out, the rest is a breeze.
STEP FOUR: On lemon number two, connect the nail to the clock's negative point. You may need to move the lemon into a new position so you can clip the nail to the clock.
STEP FIVE: Link the copper wire from lemon number two to the nail sticking out of the lemon number one. You'll see now that you've made an entire electrical circuit, from clock, to lemon, to the next lemon, and back to the clock. If all has gone well, the clock now works, because just under one volt of electricity is coursing the circuit.
If the clock does not work, make sure all connections are secure, and then double-check the directions. If several months from now the clock stops, replace the lemons, or the nails, and it should begin ticking once again.

Why it works:

The nail has been galvanized, which means it was coated with zinc to help resist rust. The lemon contains acid. This acid dissolves the zinc on the nail. In chemistry terms, this means that the zinc loses and electron and becomes a positive force. The moisture in the lemon functions as an electrolyte, a fluid that conducts electrons--if you will, a swimming pool for electrons.
The electron shoots out of the zinc, through the lemon, to react with the copper on the wire. The copper gains an electron and becomes a negative force. The exchange of electrons is a chemical reaction. It creates chemical energy, or charge. All that charge needs is a circuit.
The electron exchange buzzes around the circuit you built--zinc/nail to copper wire to clock to copper wire to nail to lemon to copper to zinc/nail to lemon, and so on. That's the transfer from chemical energy to electricity, and it gets the clock going as well as any manufactured battery.