This project will allow you to “see” the difference between AC and DC. You will need the following:
• Metal plate or pan
• Paper clip
• Piece of cloth
• Cornstarch
• Potassium iodide (available at a pharmacy)
• 9 volt battery
• 3 insulated wires with the insulation stripped off the ends
• Low voltage bell transformer (available at electronics or hardware stores)
Follow these steps:
1. Soak the piece of cloth well in a thick solution of cornstarch and water mixed with the
potassium iodide.
2. Lay the metal plate or pan with the bottom up. Wring the cloth out and lay it across the
metal plate or pan.
3. Use a wire to connect the negative terminal to one edge of the pan, using an alligator clip
or paper clip.
4. Connect the other wire to the positive end, and then slowly stroke the exposed end across
the cloth. (The electric current frees the iodine from the potassium iodide, making a dark
blue mark.) What pattern do you see? What kind of current are you using? Write your
answers.