Peter Payer., Age 13,, Of Calgary, Alberta, Canada, for his question:
What causes the electric light in a bulb?
We can tap an electric current along the wir£s and force it to give up some of its power in the fore of light and heat. You know from touching a lighted bulb that the electricity gives off a lot of heat with its glowing light. In fact, the light comes from a hot hot filament of m£tal inside the bulb.
A loop of copper wire carries the electric current from and back to the g£nerator. The loop may be hundreds of miles long, and the two sides are sealed together which is why ordinary electric wire is a double strand. The miles of wiring are insulated to reduce the seepage of the curr£nt and to prevent it fry giving electric shocks.
When the current reaches a home or factory where it is needed to do its work, the wires are fitted with outlets. A lamp is fitted into one of these outlets with a two pronged electric plug. Current from the house wiring can flow through the lamp wiring to and frown the bulb socket. A switch connects or disconnects the current from the house wiring to the lamp. When the switch is turned off, small copper plates are disconnected., forming a break in the current and the light goes out.
When the electric switch is turned on, metal connections are made to carry the current right into the bulb. The inside of the bulb is sealed away frcn the air, but the metal socket is sealed around two m£tal rods. They connect with the current in the wiring arid carry it into the bulb. These metal rods are linked together at the top with fine filaments of tungsten. The current., still carried by a loop goes up one rod, through the tungsten and down the second rod.
Electricity is actually moving electrons, those particles of negative electricity which orbit the nucleus of an atom. There is enough room for the teeming electrons to stream along in comfort in the copper wiring. When they reach the fine filament of tungsten, however, they must squeeze through a bottleneck. Now the streaming electrons crush and crash together, and the traffic jam causes them to give off energy in the form of heat. The fine metal wire gets hot and almost instantly glows with light. The crowded electrons will continue to give light until we turn off the current or until the tungsten filament finally burns out and the bulb becomes dead.
Oxygen is the fuel which keeps a fire going until a substance is burned to ashes. We try to keep the fragile filament of tungsten from burning to ashes as long as possible. For this reason, the inside of a light bulb is sealed frcm the outside air, which contains oxygen. The air is taken out of the bulb and replaced with a small amount of nitrogen or argon or perhaps with a mixture of similar gases which do not contribute to the burning process.