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
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
2.) Devices or materials that allow electrical charges to
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
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.
By John Pawlicki K8AG
The light at
How Does Electricity Know to Light Up a Light Bulb?