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asked Jan 23 in Engineering & Technology by (360 points)

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answered Jan 23 by (1.3k points)
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Light Dependent Resistor(LDR) is a component that has a (variable) reistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits.

Also,

A Passive Infrared Resistor (PIR) is an electronic sensor that measures infrared light radiating from objects in its feild of view. They are most often used in PIR-based motion-detectors.

Ref: wikipedia.org
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