Could someone please explain why the resistance decreases when the temperature and light intensity increases in a thermistor and LDR?

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Could someone please explain why the resistance decreases when the temperature and light intensity increases in a thermistor and LDR? I don't understand why it decreases. Shouldn't it increase. Becuase in the graphs, pd divided by current equals resistance right. The resistance graphs go up, not down. Help!!!

Posted Fri 6th April, 2012 @ 13:08 by Tahira xx

1 Answer

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These are both Potential Dividers but the simplest answer is that Thermistors are made out of a semi conductor metal which has improved conductivity with increased temperature. This is the same case for LDRs which conduct more electricity when the number of Lumens (Measure of light intensity) increases. I believe they are made of Smart metals which is why they have these properties. Normal wires possess the properities which you would expect, so increased temerature increases the resistance but this isn't the case. 

If your're interested further, LDRs exhibit photoconductivity and Thermistors exhibit Thermoconductivity.

I hope this answers your question :) 

Answered Fri 6th April, 2012 @ 16:37 by Bhavik