James Eacho, age 13 of Spokane, Wash., for his question:
What makes a neon sign?
A neon sign is a glass tube connected to an electro current. The air has been removed from the tube and replaced with a little neon gas. When the current is turned off the neon gas in the tube is colorless and invisible. When the current is turned on, the neon gas is agitated. And when neon gas is agitated, either by heat or electric current, it glows with a lovely orange‑red color.
The glass tube which contains the neon can be twisted and bent. It can be made to write letters and words. Blank spaces are left between letters and words to spell out SODA FOUNTAIN or JOE'S DINER. The orange‑red of neon is bright enough to shine at high noon. After sunset, it can be seen for miles.
Only neon can cause that cheerful red color. For each gas lights up with a color of its own, Scientists identify a substance from the color it gives off when agitated. The substance to be tested is heated in a clear flame or bolted with electricity. The light it gives off is analyzed with a spectroscope, an instrument with a prism between taro lenses.
The spectroscope grades and identifies the colored glow. For example both lithium and rubidium give off a red glow. Human eyes might be unable to tell which red was which. The spectroscope spreads the red into a rainbow spectrum. The expert sees that one red is composed of one part of the spectrum, the other red from another part of the spectrum. He knows which element he is dealing with.
Neon gas gives off its own special red‑orange glow when heated or jogged with a jolt of electricity, giving its atoms an extra nudge. The activity takes place in the electrons which circle the nucleus of the neon atom. Electrons circle the nucleus much as planes circle the sun. There are ten electrons in the neon atom. Two form an inner shell around the nucleus and eight form an outer shell.
In the neon atom, the two electron shells are complete. We call these electron shells energy levels. Electrons are very energetic particles. much energy is used to keep going in the inner shell, so much to keep going in the outer. This normal state of affairs is upset when the neon atoms get an extra jolt of energy.
The electrons in the outer shell swing outside their orbits. The electrons in the inner shell may swing out into the outer shell. The whirling electrons are now charged with an extra jolt of energy. But this does not make them glow.
Sooner or later, this extra energy is spent. The electrons must fall back into their normal orbits, To do this, they must give up their extra jolt of energy. The neon atom gives up this energy in the form of a red-orange glow, and we can enjoy its cheerful light along our streets and highways.