Manufacture:

The tungsten filament in a modern light bulb is supported by several molybdenum wires. The ends of the support wires are imbedded in a glass button at the top of the glass support rod. The copper and nickel lead-in wires, which carry the current to the filament, are supported by a glass support stem. One lead-in wire is soldered to the metal contact at the base of the bulb, while the other is electrically connected to the side socket contact. The contacts are separated by an insulating plate. An electrical current can pass in either direction through the filament.

During manufacture, the bulb is evacuated through the exhaust tube and filled with nitrogen/argon gas. The bulb is partially re-evacuated and the lower end of the tube heat-sealed. The lead-in wires are soldered to their contacts and the glass bulb cemented to the threaded metal base.

Familiarize yourself with the components of a modern light bulb using the diagram below. Point to the individual components in the components list to locate them in the diagram.

Components in a modern incandescent light bulb

Light Emission:

Light is generated in a light bulb when an electric current passes through a filament, which heats the filament white hot.

Current can pass in either direction through the filament. The current flows through the filament through the lead-in and support wires. Use the Variable Current Light Bulb applet on the right hand side to explore how raising and lowering the current affects the brightness of the bulb and temperature of the filament.

After you have explored the applet, take the quiz on the right hand side. You can always go back and experiment with the applet, to answer the questions.