Paul Vitruk, age 13, of Philadelphia, Pennsylvania, for his question:

What makes the light in a bulb?

Electricity is created by the motions of electrons, those negatively charged particles that swarm around the nucleus of the atom. A generator provides the voltage that jolts them through a wire circuit. They use this voltage energy to jog and jostle or skip from one atom to another. This electron activity creates the current in the wires.

The circuit of activity is carried in a double strand of copper wires, where the frantic electrons have room to move. But when the wire is adjusted to carry the current through a light bulb, the traffic runs into a bottleneck. The same number of moving electrons suddenly is squeezed into the much thinner filament inside the bulb. Friction from myriad minuscule collisions generates heat and the metal filament glows with light. When about three billion billion electrons try to squeeze through the bottleneck, they create enough heat energy to light a reading lamp