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    http://www.edexcel.com/migrationdocu...e_20110606.pdf

    I need help on question 5. A is the correct answer, but I need an explanation for why. Decreasing temperature makes the thermistor's resistance increase. Therefore pd across the thermistor increases. So why isn't D the right answer? Also isn't the current in the circuit constant?

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    What is it that makes you think that the current would be constant? What determines the current in a simple circuit like this, where there is just a single component and an ideal battery?
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    (Original post by krisshP)
    QP
    http://www.edexcel.com/migrationdocu...e_20110606.pdf

    I need help on question 5. A is the correct answer, but I need an explanation for why. Decreasing temperature makes the thermistor's resistance increase. Therefore pd across the thermistor increases. So why isn't D the right answer? Also isn't the current in the circuit constant?

    Thank you
    Considering a series circuit, if resistance increases, current decreases. Voltage of source remains unchanged, and potential drop across resistance is unchanged. But this is only true if they're in series..
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    So is voltage across the thermistor constant and equal to the cell's emf? Since sum of all potential differences=emf of cell. If voltage is constant across thermistor, by V=IR, a resistance increase means a decrease in current. So A is correct. I thought voltage was affected by resistance. Sorry I'm terrible at electricity
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    The potential difference across a component may well be affected by its resistance, but you have to look case-by-case at which quantities will change and which will stay the same. In this case, you've now got it - Kirchhoff's Second Law tells you that the p.d. across the thermistor will always be the same as the emf of the cell, so the change in resistance will bring about a change in current.
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    (Original post by Pangol)
    The potential difference across a component may well be affected by its resistance, but you have to look case-by-case at which quantities will change and which will stay the same. In this case, you've now got it - Kirchhoff's Second Law tells you that the p.d. across the thermistor will always be the same as the emf of the cell, so the change in resistance will bring about a change in current.
    Thanks
 
 
 
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