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Voltages in Potential Divider

  1. Apr 29, 2008 #1
    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

    Attached Files:

  2. jcsd
  3. Apr 29, 2008 #2


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    Gold Member

    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.
  4. Apr 29, 2008 #3


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    Staff Emeritus
    Science Advisor

    Sometimes it takes a while for a mentor to spot the attachment to approve it-- an hour's not bad going!
  5. May 1, 2008 #4


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    Gold Member

    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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