Nuts and Volts - September/October 2018

60 September/October 2018

Turn on a light switch. Assuming that you’re living where electricity is available and someone has paid the electric bill, the light will come on. Turn it off and the light goes off again. Electricity seems to be smart enough to light the light bulb, while leaving the rest of the apparatus — the switch, wires, fuses in the fuse box, and pole transformers, etc. — alone.

#1: How does electricity know to light the bulb while leaving everything else dark?

The light bulb must be different than the rest of the equipment. What differences cause electricity to ignore all that equipment but have such a pronounced effect on the light bulb?

If everything is working as it should — other than the light bulb — all of the other equipment must either conduct electricity (pass charges with very little restriction like the wires, metal parts of the light fixture, and the closed switch) or stop electricity (like the surrounding air, plastic, and ceramic parts of the light fixture, etc.).

Conductors (like wires) allow electricity to flow with little pressure. Insulators (like air) stop the flow of electricity completely. Using conductors and insulators, electricity is channeled to pass through the device that we want to use power to generate light: the light bulb.

The light bulb must have something that these other devices, wires, switches, transformers, etc., do not.

For devices to use power from electricity, they must neither completely stop nor freely allow the flow of electrical charges. For the most part, we can think of three different types of things:

1.) Devices or materials that stop electrical charges from moving.

2.) Devices or materials that allow electrical charges to move freely.

3.) Devices or materials that restrict but not prevent electrical charge flow.

The most interesting devices and materials are those in the third category.

The characteristic of a device that restricts charge flow is called resistance.

Too much resistance and a device can effectively stop charge flow, as with switches turned off, air surrounding the devices, coating on wires, etc. Too little resistance and charges simply pass through the device as with wires and Pawlicki’s Posers

This is the first in a series of questions to encourage readers to think about electricity and electronics in ways that, perhaps, they had not before. My intent is to improve understanding on how electricity behaves and how it can be made to do what we want.

These kinds of questions rarely show up on high school or even college exams, yet they demonstrate an understanding of electronics beyond the formulas. I hope these questions help people get a real feel for how electricity works.