The cheap plastic disc on your ceiling is doing real physics — and one common type contains a tiny speck of radioactive material. This short course explains the two ways smoke detectors sense a fire (an ionization current broken by smoke, and a light beam scattered by smoke), why each catches different kinds of fires, and how to keep yours working — including why a smoke alarm is not a carbon-monoxide detector.
The cheap plastic disc on your ceiling is doing real physics — and one common type contains a tiny speck of radioactive material. This short course explains the two ways smoke detectors sense a fire (an ionization current broken by smoke, and a light beam scattered by smoke), why each catches different kinds of fires, and how to keep yours working — including why a smoke alarm is not a carbon-monoxide detector.
