Question

Explain in terms of particle behavior why smoke particles cause the detector alarm to sound

Answer 1

Smoke particles disrupt the ion flow created by americium-241 in smoke detectors, causing a drop in electric current and triggering the alarm. This mechanism helps in early fire detection and increases safety.

Step-by-step explanation:

Inside a smoke detector, a tiny amount of the radioactive element americium-241 emits α-particles, which ionize the air and create a small electric current between two metal plates. This continuous ionization forms the basis for detecting smoke. When smoke particles from a fire enter the detector, they impede the flow of ions, thus reducing the conductivity of the air and causing a significant drop in the current. This decrease in current level is detected by the circuit, which then triggers the alarm to alert of the potential danger of a fire.

Regular battery replacement is recommended as the continuous drain of current by the ionization process depletes the battery over time, irrespective of alarm activation. The americium-241 is sealed in plastic within the detector, making it harmless unless tampered with.

Answer 2

Smoke detectors are of many types but they rely on the principle of diffusion of smoke. Diffusion is the movement of particles from a region of high concentration to a region of lower concentration. Smoke particles move in what is known as Brownian motion.