This smoke detector is fitted to the ceiling of a workshop. Fig. 1 shows the source chamber inside the detector. A tiny radioactive source emits alpha parti...
Question 1 Report
This smoke detector is fitted to the ceiling of a workshop. Fig. 1 shows the source chamber inside the detector. A tiny radioactive source emits alpha particles that ionise air molecules. A small current normally flows between two metal plates. Smoke absorbs some alpha particles, so fewer air particles are ionised and the alarm circuit responds. The source is sealed so that radioactive material cannot enter the room.
(a) What type of radiation is used in the detector? [1]
(b) Which particles make up an alpha particle? [2]
(c) Describe why the current decreases when smoke enters the chamber. [2]
Answer Details
(a) The detector uses alpha radiation. [1]
(b) An alpha particle is made of two protons and two neutrons. [2]
(c) Smoke absorbs or stops alpha particles. Consequently, fewer air molecules are ionised, so there are fewer charged particles available to carry current between the plates. The current therefore decreases. [2]
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