Circuit with a Switch

• 6-volt battery
• Low-voltage incandescent lamp (Radio Shack catalog # 272-1130 or equivalent)
• Long lengths of wire, 22-gauge or larger
• Household light switch (these are readily available at any hardware store)

Household light switches are a bargain for students of basic electricity. They are readily available, very inexpensive, and almost impossible to damage with battery power. Do not get "dimmer" switches, just the simple on-off "toggle" variety used for ordinary household wall-mounted light controls.

Lessons In Electric Circuits, Volume 1, chapter 1: "Basic Concepts of Electricity"

• Switch behavior
• Using an ohmmeter to check switch action

Build a one-battery, one-switch, one-lamp circuit as shown in the schematic diagram and in the illustration. This circuit is most impressive when the wires are long, as it shows how the switch is able to control circuit current no matter how physically large the circuit may be.

Measure voltage across the battery, across the switch (measure from one screw terminal to another with the voltmeter), and across the lamp with the switch in both positions. When the switch is turned off, it is said to be open, and the lamp will go out just the same as if a wire were pulled loose from a terminal. As before, any break in the circuit at any location causes the lamp to immediately de-energize (darken).