Spark Visibility
The light emitted by a spark does not come from the current of electrons itself, but from the material medium fluorescing in response to collisions from the electrons. When electrons collide with molecules of air in the gap, they excite their orbital electrons to higher energy levels. When these excited electrons fall back to their original energy levels, they emit energy as light. It is impossible for a visible spark to form in a vacuum. Without intervening matter capable of electromagnetic transitions, the spark will be invisible (see vacuum arc).
Read more about this topic: Spark Gap
Famous quotes containing the words spark and/or visibility:
“I wouldn’t take the Pope too seriously. He’s a Pole first, a pope second, and maybe a Christian third.”
—Muriel Spark (b. 1918)
“My children have taught me things. Things I thought I knew. The most profound wisdom they have given me is a respect for human vulnerability. I have known that people are resilient, but I didn’t appreciate how fragile they are. Until children learn to hide their feelings, you read them in their faces, gestures, and postures. The sheer visibility of shyness, pain, and rejection let me recognize and remember them.”
—Shirley Nelson Garner (20th century)