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    The markscheme says it all.

    For a semiconductor (graphite, in the pencil), heating - in this case by the current - frees more electrons to carry charge and thus the resistance decreases.

    Don't confuse it with the effect in metals, where an increase in temp causes an increase in resistance.
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    (Original post by phys981)
    frees more electrons to carry charge and thus the resistance decreases.
    Yes but then shouldn't more number of electrons result in more current and that should result in less resistance? Why is it the other way around?
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    It's not the other way round - are we looking at the same question???

    Semi conductors + increased temp = more free electrons, therefore more current and less resistance.

    metals + increased temp = higher resistance and lower current
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    Oh... Sorry for the trouble and thank you sm
 
 
 
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