Resistors and Switches

After making some simple circuits, we were ready to learn about resistors. First we made a simple "dimmer switch" using a wire coiled around a pencil. (See here for supply list.) As you move the connection up and down the coiled wire (allowing the current to either go through a lot of wire, or just a little wire), you adjust the resistance and the light gets brighter or dimmer accordingly.

We also made a circuit that included a large piece of paper towel. The paper towel provides enough resistance to the current that the electricity doesn't even get through, and the bulb won't light. But if you wet the paper towel, it provides less resistance (water helps the paper towel become somewhat of a conductor) and the bulb lights---dimly. If you sprinkle salt onto the wet paper towel, you decrease resistance even further and the light glows quite brightly!

Next, we experimented with switches. Here is a simple on-off switch using a paper clip.

My favorite was the three-way switch, which is a concept I have never before understood. This is like a room in your house where there are two switches (one at each end of the room) to turn on the same light. Here's how it works: there are basically two circuits, a short one and a long one, and two switches that toggle between the two circuits. If one switch is "up" and the other is "down," neither circuit is complete and the light is off.

If both switches are "up," the shorter circuit is complete and the light turns on.

If both switches are "down," the longer circuit is complete and the light turns on.

Amazing, eh? I love it.