Susan Moeller, age 10, of Huntsville, Ala., for her question:
HOW DOES A LIGHT BULB WORK?
An electric light bulb sheds a calm and steady light. You might never suspect that it is designed to create a fantastic traffic jam. Nevertheless, this is just what happens. The frantic activity takes place on a minuscule scale, far too small to be seen by human eyes.
Electric current is created by zillions of moving electrons. Normally these mini particles of matter are attached to atoms, where they swarm around in orderly traffic lanes. Electric current is created when billions of electrons are shaken loose and go hopping through the wires. A lamp bulb is designed to plug into an electric current and change some of its energy into light.
Inside the light bulb are two sturdy metal prongs, connected by a fine filament made of a metal called tungsten. The glass seals the whole thing from the outside air. The metal base of the plug screws into an electrical outlet, and an electrical switch turns the current on and off.
When the current is switched on, billions of jogging electrons swarm up through the prongs and the filament inside the bulb. They have plenty of room to stream through the sturdy prongs. But when they reach the fine filament, they are crowded into a bottleneck. Imagine what would happen if the speeding traffic on a wide freeway suddenly was crowded into one narrow lane.
Naturally there would be a disastrous traffic jam, with blazing cars all over the place. Electrons crowding through the filament in a light bulb create a somewhat similar traffic jam. As they speed along, they jostle atoms of tungsten in the filament and this jostling motion creates heat. The filament becomes so hot that it glows and sheds light.
This magic occurs because electrons are shaken free from the tungsten atoms. When a tungsten atom loses an electron from an inside traffic lane, an electron from an outer lane hops in to take its place and gives off a small glow. Multiply this tiny glow by several billion, and you have enough razzle dazzle to light up an electric bulb.
Glowing heat of this kind tends to weaken a metal and cause its atoms to break apart. Tungsten is able to withstand more heat than most metals but eventually the filament breaks and the bulb burns out. In the presence of oxygen, it would burn out sooner. This is why the inside of the bulb has a sealed in mixture of argon or other gases that do not boost the burning process.