Page 11 - Curriculum Visions Dynamic Book

antioxidant: a substance that prevents oxidation of some other substance.
How a light bulb works
Light bulbs (incandescent bulbs) rely on the light given out by a filament as it gets very hot. The first attempts to make an incandescent bulb were a failure because the filament was left
in air, where it reacted with the oxygen and burned away within seconds.
To try to solve this problem the filaments were put in a glass bulb from which as much air as possible had
been withdrawn. But this was not
very successful either. A vacuum is difficult to produce, and should a
bulb break, the resulting implosion
of the glass can cause possible
harm to anyone standing nearby.
But even if it didn’t break, the
glass quickly blackened and so
became unusable. This is because
the hot filament sends out a stream
of particles, gradually wasting away (and thus producing a short light
bulb life). Particles of metal were deposited on the inside of the glass bulb, thus darkening it and allowing less useful light to get out.
Both of these disadvantages were
overcome using nitrogen gas. By filling the
bulb with nitrogen, oxygen is automatically pushed out. This means that the filament will not burn away. At the same time the presence of gas inside the bulb means that a low pressure is not needed and the bulb won’t implode if
it breaks.
The nitrogen also helps to give the filament
a longer life. As particles (atoms) of metal try
to leave the hot filament, they find themselves surrounded by molecules of nitrogen gas. The result is there is a much greater chance that the metal atoms will simply bounce back on to the filament again. Not only does this help preserve the filament, but it also means that fewer atoms reach the glass bulb to darken it.
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