A rheostat is another name for a variable resistor. This simple component drops a certain amount of voltage in a circuit, which is proportional to the adjusted position. It is often used in dimmer switches for chandeliers, model train control packs and volume adjusters on stereos, to name a few. A simple version of a rheostat is also used frequently for school science fair projects and in the classroom for the purpose of illustrating variable resistance.
Things You'll Need
- Oxidized door spring
- 18 AWG solid wire
- 3 alligator clip test leads
- Wire cutter
- Wire stripper
- Piece of scrap lumber longer than door spring
- Staple gun with staples
- 9-volt battery
- Hobby light bulb in socket
Mount the spring to the piece of scrap lumber. Keeping the spring coils together, hold it to the board with one hand and using the other hand, staple each end of the spring. One staple for each end should be sufficient.
Create the wiper wire. Cut about a 3-inch piece of wire with the wire cutter. Using the wire stripper, remove about 1 inch of the insulation jacket on either end.
Connect a test circuit. Clip one end of an alligator clip test lead between the positive terminal of the 9-volt battery and the other end to one end of the spring, which now serves as the rheostat coil. Another test lead should connect between one end of the wiper and one connector on the hobby bulb socket. A third test lead should connect between the other hobby bulb socket and the negative terminal to the battery.
Test the rheostat. Holding the insulated part of the wiper you made in Step 2, touch the free end of it to the coil and vary its position. Notice how the brightness of the bulb varies based on the position of the wiper distance from the direct connection between the battery and coil.
Tips & Warnings
- The spring must be oxidized, because a shiny metal spring will not resist current flow very well.
- The piece of scrap lumber should be thick enough so that the staples do not go through to the bottom side of the board.
- School-aged children who are working on this type of project should do so under the supervision of a parent or other responsible adult.
- Wear safety glasses when using the staple gun.
- Photo Credit volume image by Bernard BAILLY from Fotolia.com
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