Which statement best describes how a Photoelectric Smoke Detector detects smoke?

Which statement best describes how a Photoelectric Smoke Detector detects smoke?

• A. Photoelectric Smoke Detector detects smoke primarily through light scattering by smoke particles.
• B. Photoelectric Smoke Detector detects smoke by ionizing air.
• C. Photoelectric Smoke Detector detects smoke by flame detection.
• D. Photoelectric Smoke Detector detects smoke by heat sensing.

Answer: (A)

The key idea is that photoelectric smoke detectors sense smoke through light scattering. Inside the detector a light source shines within a chamber, and the light is arranged so it normally misses the sensor. When smoke particles enter, they scatter the light and some of it is directed to a photosensor, triggering the alarm. This relies on how smoke interacts with light, not on changing electrical current from ionized air or on sensing heat or flame radiation. In contrast, detectors that ionize air look for changes in electrical current caused by smoke ions, flame detectors detect radiation from flames, and heat detectors respond to a rise in temperature. Photoelectric detectors are particularly quick to respond to smoldering, smoky fires with larger particles.

The key idea is that photoelectric smoke detectors sense smoke through light scattering. Inside the detector a light source shines within a chamber, and the light is arranged so it normally misses the sensor. When smoke particles enter, they scatter the light and some of it is directed to a photosensor, triggering the alarm. This relies on how smoke interacts with light, not on changing electrical current from ionized air or on sensing heat or flame radiation.

In contrast, detectors that ionize air look for changes in electrical current caused by smoke ions, flame detectors detect radiation from flames, and heat detectors respond to a rise in temperature. Photoelectric detectors are particularly quick to respond to smoldering, smoky fires with larger particles.