Concept explainers
Usage of photoelectric circuit in burglar alarm, a smoke detector and in photographic light meter.
Explanation of Solution
(a)A burglar alarm:
The alarm consist of a photoelectric cell connected in a closed electrical circuit and an infrared source of light. The light from the infra red source is continuously incident on the photoelectric cell, maintaining a constant current in the circuit. The device is kept conceated near the place to be protected.
If a burglar intercepts the invisible infrared rays, the photoelectric current stops. This automatically operates a relay,which sends an
(b)A smoke Detector:
A light beam could be focused on a photocell. When the light beam is interrupted by a smoke as it become denser and denser (thicker)then the current in the (thicker)circuit would decrease or stop. An alarm could be set to go off when the current decreased below a certain level.
Many smoke detectors use the
(c)Photographic light meter:
The amount of current in the circuit depends on the intensity of light, as long as the
Chapter 27 Solutions
Physics: Principles with Applications
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