Why does closing the switch cause the voltage across the thermistor to decrease?

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Homework Help Overview

The discussion revolves around a circuit involving a thermistor and a switch. The original poster questions why closing the switch results in a decrease in voltage across the thermistor, considering the changes in resistance and current flow in the circuit.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to reason through the relationship between the switch, the bulb, and the thermistor's resistance. Some participants express uncertainty about the circuit's layout due to a missing attachment, which may hinder their ability to contribute effectively.

Discussion Status

Participants are exploring the implications of closing the switch and its effect on the thermistor's voltage. There is a lack of explicit consensus, but some lines of reasoning are being discussed regarding current distribution and resistance changes.

Contextual Notes

There is a noted absence of a visual representation of the circuit, which may limit the clarity of the discussion. Participants are also considering the behavior of the thermistor under varying resistance conditions.

nokia8650
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See attachment.

Question: "The switch S is now closed. Explain, without calculation, why the voltage across the
thermistor will fall"

I am able to deduce that by turning the switch on, the bulb becomes part of the circuit, effectively loweing the resistance of the parrallel "section" and hence the resisitance of the overall circuit. This will cause a greater current to flow. Why, however, will the voltage across the thermister fall? Thanks
 

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I can't see the picture so I don't know what the circuit looks like. Try uploading it to imageshack and putting in a link or something like that.
 
madmike159 said:
I can't see the picture so I don't know what the circuit looks like.

Sometimes it takes a while for a mentor to spot the attachment to approve it-- an hour's not bad going!
 
Wellif theresistanceof the thermistor was high then most of the current would go round via the bulb. If the resistance in the thermistor droped low enough then the bulb should go out.
 

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