In a photoelectric smoke detector, what causes electric current to conduct?

In a photoelectric smoke detector, the detection mechanism relies on the presence of smoke particles in the air. When smoke enters the sensing chamber, it scatters light from a light source, typically a light-emitting diode (LED). This scattering effect alters the light intensity that reaches a photodetector within the device.

When there is no smoke, the light beam travels directly to the photodetector with minimal interference, resulting in a low or non-existent electric current. However, when smoke is present, the scattered light causes an increase in the electric current conducted by the photodetector. This change in current serves as a signal that smoke is present, triggering the alarm.

Thus, the presence of smoke is crucial because it directly impacts how light behaves within the detector, leading to the conduction of electric current that activates the smoke alarm.