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Q & A: light dependent switches

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Most recent answer: 04/14/2017
Q:
Hi I am a bit confused about a certain aspect of physics which is to do with light dependent resistors in circuits. I have been told that if light shines on the component the resistance is low and in darkness the resistance is highest. What I am confused with is that if these LDRs are used in the circulatory of automatic lights then how would they work? In darkness the lights would need to come on. But when its dark the resistance is high so how will the current pass through to turn on the light? Same vice versa. In daytime the resistance is low so wouldn't that mean the light would be on since current can now pass through and turn on the light? Sorry if I am missing something here but I would love this clarified! Thanks.
- Daniel (age 16)
London
A:

The current to drive the automatic light doesn't flow through the sensor. The small current through the sensor is used to control a switch for the automatic lights.

Mike W.


(published on 04/14/2017)

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