Ionization smoke detectors activate when what occurs?

Ionization smoke detectors operate based on the principle of detecting changes in electrical conductivity caused by smoke particles. Inside the detector, a small amount of radioactive material ionizes the air, creating charged particles that allow a continuous flow of current between two electrodes. When smoke particles enter the detection chamber, they attach to these ions, which disrupts the flow of current. This obstruction of the electrical current is what triggers the alarm.

The primary function of an ionization smoke detector relies on this mechanism of current interruption due to the presence of smoke, making the option about smoke particles obstructing the current flow the correct answer. Understanding this principle is critical, as it distinguishes ionization detectors from other types, such as photoelectric detectors, which use light reflection rather than current interruption to detect smoke.