An LED (This project works best with an LED that has a low voltage and low current)
Instructions
Roll a patch of paper towel around a zinc nail and wind a 12" copper wire on top of that. Leave a 4" tail of wire. Make eight of these.
Push the nails into the cork radially. (If you have trouble, you can drill small holes in the cork first.) Next connect the petal battery cells in series by connecting the positive (copper) end of one cell to the negative (zinc) end of the next cell. To do this, connect a copper wire tail to its neighboring nail's head. Be sure to make a good connection: wrap the wire tightly at least four times around the nail. Continue connecting tails to heads. However, don't connect the last tail! Doing so would cause a "short circuit" that could damage your battery. The last tail and nail head will be connected to the LED in the next step.
LEDs need to be connected with the correct polarity; that is, connected in a circuit with positive-to-positive and negative-to-negative wiring. Look carefully at your LED and you will see that one lead is longer than the other. This is the positive lead. Connect it to the positive lead of your battery, which is the last (unconnected) copper tail. Twist the positive lead of the LED onto the last tail of your battery. Be sure to intertwine the leads so that they have a good connection.
Twist a 2" length of copper wire around the LED's negative lead, and wrap the other end around the remaining unconnected nail head (which is your battery's negative connection).
The moment of truth! Place a drop of lemon juice on each petal's paper towel. When all of the petals are moistened, the LED should light. Yay!If the LED doesn't light, check that all of the connections are good. Make sure that on each petal, the copper wrapped around the paper towel is not touching the copper wrapped around the nail head.The LED should stay lit for half an hour or so until the paper towels dry out. You can light it up again simply by adding more lemon juice. Try adding a stem, leaves, and a flower pot. Try using other kinds of metal. Try making the petals out of metal foil instead of wire. Experiment! Have fun!
Science Behind It
This has the same basic principals of the lemon battery project. The lemon juice is very acidic. Its pH level ranges from 2-3, anything less than 7 on the pH scale is considered acidic. The common battery pH level is 1. The reason why the lemon juice works as a battery is because the acid in the lemon juice reacts with the copper and zinc to create an electrochemical reaction which generates a small potential difference which exchanges electrons to reach a lower energy state, this creates the electric current to power things.
Tips
This project can be incorporated into an arts and crafts project, and you can have the members build any shape they want. Just keep in mind that the wires need to be touching the nails and that the wires need complete the electrical circuit for any shape to work.