Explore electricity using an unexpected material! Learn about circuits and conductive materials as you use playdough to create a circuit that lights an LED.
Time: 40 - 50 minutes (20 min. prep + 20 - 30 min. activity)
Topics: circuits, dough, conduct, electricity
What you need:
- Ingredients for conductive playdough (adult supervision suggested):
- Cream of tartar (optional)
- Vegetable oil
- Food coloring
- 5mm LED bulbs (available from sites like Amazon, RadioShack, or SparkFun)
- 9V battery and battery clip or snap (also available from sites above)
What to do:
1. Prepare the conductive dough. You can do this ahead of time and store it until later.
- Mix together in a pot: 1 c. flour, 1 c. water, ¼ c. salt, 3 T. cream of tartar, 1 T. vegetable oil, and a few drops of food coloring. Note: The cream of tartar acts as a preservative. It can be left out, but the dough will not last as long.
- Heat over medium heat, stirring constantly, until the dough forms a ball in the middle of the pot.
- Remove from heat, cool, and store in plastic wrap or a sealed container until needed. It will last about a week in proper storage (less without the cream of tartar added).
2. Think about what you already know about electricity. What kinds of machines or devices are powered by electricity? Where does the electricity come from? What kinds of materials help the electricity get from one place to another? Instead of wires, you will be using the conductive dough you made to connect a battery to a light bulb and create a circuit.
3. To make a simple dough circuit, use a 9V battery with a clip or snap attached, one LED bulb, and a ball of dough about the size of a ping-pong ball. Split the ball of dough into two pieces.
4. Lay out the circuit: connect the positive lead of the battery into the first piece of dough, the positive (longer) leg of the LED also into the first piece of dough, the negative (shorter) leg of the LED into the second piece of dough, and the negative lead of the battery also into the second piece of dough. Safety note: Never connect the LED bulb directly to a 9V battery without the dough in between, as the battery has too much voltage. The bulb will burn out and could possibly explode.
5. Make some observations about your circuit. Is electricity flowing from the battery to the light bulb? How can you tell? Trace the path of the electricity with your finger to see if it makes a complete circle. There should be just one path out of the battery and one path back into the battery. If electricity is not flowing to your bulb, check the following things:
- Check that the dough balls are not touching each other.
- Make sure the positive ends of the LED and the battery are both connected to one piece of dough, while the negative ends are both connected to the second piece of dough. (Remember, the longer leg of the LED is the positive one and the shorter leg is the negative one.)
6. Try moving your circuit so that the dough balls touch each other. What happens? Trace the electricity’s path with your finger again. Is there a path the electricity could follow that doesn’t go through the light bulb?
7. Now get creative with your circuit:
- What kinds of shapes or creatures could you make with your dough pieces?
- How many LEDs can you add and still get them to light up?
- How could you add extra features or designs without interrupting the circuit? (Hint: The dough conducts electricity, or helps it to flow. Are there materials that might insulate, or stop the electricity from flowing in a certain direction?)
8. Another idea to try: Make some dough that insulates instead of conducting electricity. (See the recipe below.) How does it behave differently from the conducting dough? What new creations can you make with this dough?
- Make sure all your measuring tools, mixing spoon, and bowl are very clean.
- Use distilled water, not tap or bottled water. Mix 1 c. flour and ½ c. white sugar in a mixing bowl. Add 3 T. of vegetable oil and mix thoroughly. Now add one tablespoon of distilled water at a time until the dough forms bean-sized clumps.
- Transfer the lumpy dough onto a clean surface and knead into a ball. Add more water, one tablespoon at a time and knead. Continue adding water until the dough becomes sticky. Now knead in more flour until the ball stops feeling sticky and reaches the texture of playdough.
- Store in plastic wrap or an airtight container. It will last about a week. The more it is handled the more conductive it will become.
An electric circuit is a path that allows electricity to flow from a source of electric current. Along the way, the electric current may be used to light a light bulb, power a motor, or run an electronic device. A circuit needs a few different pieces:
- A source of electric current, like a battery or electrical outlet
- An output—the light bulb, motor, or whatever will be powered by the electricity
- Conductive materials like wires, metal, or water to carry the electricity between the source and output
In order for the current to flow, the circuit must be closed, creating an uninterrupted loop from the source to the output and back. (Notice how “circuit” sounds a lot like “circle?”) If the circle is broken, the electrical current will not flow. If there is more than one path for the electricity to follow, it creates a short circuit. You did this in your first dough circuit when you pushed the dough balls together to make them touch. The electricity could flow straight from one dough ball to the other, skipping the LED completely.
Some materials, called conductors, allow electricity to travel through them easily. Other materials, called insulators, do not allow electricity to pass through them. Electrical cords, for example, are usually made of metal (a conductor) covered with plastic or rubber (an insulator). Electricity can travel through the wire, but the coating stops it from traveling into anything else that touches the wire (like your hand!) The mixture of salt and water in this dough makes the dough a good electrical conductor. The insulating dough recipe replaces the salt with sugar, which does not conduct electricity as well as salt. The distilled water is important also, because even the extra minerals found in tap water can be enough to make the dough conduct some electricity.