Which type of detector is activated by smoke interrupting a beam of light?

The correct answer is the photoelectric detector. This type of detector operates based on the principle of light interruption. It features a light source that emits a beam of light, typically a light-emitting diode (LED) or a laser, and a photoelectric sensor that detects this light. When smoke particles enter the detection area, they scatter the light beam. This scattering effect causes a drop in the intensity of light reaching the sensor, triggering the alarm.

Photoelectric detectors are particularly effective at sensing smoldering fires, which produce more smoke than flames during the early stages. Their design makes them well-suited for environments where slow-burning fires might occur, thus providing early warning and potentially preventing greater damage.

In contrast, fixed temperature detectors respond to changes in temperature beyond a predetermined threshold, while rate of rise detectors activate based on the speed at which the temperature increases. Ionization chamber detectors operate using radioactive material to detect smoke rather than light interruption, being more sensitive to fast-flaming fires.