Charged Up About Learning?

Build a switch

Ages: 10 and up
Materials: Empty thread spool. Small piece of aluminum foil. Old tin can. Two small wood screws. One long wood screw. Two metal washers. Piece of wood about 2 inches square. 6-volt lantern battery. 6-volt lantern flashlight bulb. Small socket for the bulb. Some insulated wire.
Time Required:2 hours

Lewis Latimer invented a switch to control an electric light bulb. The switch mechanism was a bit unusual: when the knob was turned, a metal pin came between two metal strips to complete the circuit.

You can build a switch that works in much the same way ... and use it in the electrical experiments that we'll talk about later. Since you will need three switches for the parallel circuit experiment, gather together enough material to build three switches before you begin.

Homemade Electrical Switch

Our switch does not use a metal pin. Instead, a metal foil surface on its "knob" comes between two metal contact strips to complete the circuit. Here's how to build it:

Use an empty thread spool as the knob. As shown in the drawing, glue a small piece of aluminum foil between the two end flanges. The piece of foil should run a little over halfway around the spool.

This is important: apply cement all over the back of the piece of foil so that all of the foil is held tightly against the wooden surface. The foil must fit smoothly in place with no bubbles or tears.

Switch with Battery and Light Bulb

Make the two contact strips out of metal cut from a tin can. Clean the can thoroughly, then remove both ends. Next, cut the can open lengthwise with tin snips and press it flat. The cut edges will be sharp, so work carefully.

Each contact strip should measure about 1/2 inch by I inch. Bend each strip into an 'L' — each leg of the 'L' should be about 1/2 inch long.

The switch's base is a piece of wood about 2 inches square. Mount the knob on the center of the base with a long wood screw. Place a washer at the top and bottom of the spool. Tighten the screw just enough so that the knob can't jiggle around but will still turn freely.

Mount the contact strips on the base with short wood screws. The upward-pointing legs of the "L s" should press gently against the spool like bookends against a book. The top of each leg should press gently against the spool's middle.

Observe the action of the switch. As you rotate the knob, the metal foil comes in contact with both contacts ... at this point the switch is "on."

Turn the knob further and the foil moves past one of the contacts to break the circuit... the switch is "off."

To connect the switch to other components, simply loop the interconnecting wires underneath the screws that hold the contacts in place.

Just about the simplest possible electric circuit is shown in the second diagram. It consists of a switch, a light bulb (held in a socket) and a battery. Observe how the switch controls the current flowing through the circuit and turns the light on and off.

Part two

Remember to play it safe around electricity. Use caution and wear safety glasses and other appropriate dress when building and performing experiments.