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    MS
    http://www.scribd.com/mobile/doc/46124583?width=768
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    http://www.scribd.com/mobile/doc/50654250?width=768

    I need help on question 18.

    With the first part why do you need a variable power supply/variable resistor?

    In cii why can't you say
    In I=nAvq the n value increases as there are more free electrons per metre cubed
    With I, A and q constant, drift velocity decreases??
    How do I know whether I am supposed to say this or say that there are more atomic vibrations, ausing more collisions between atoms and electrons, so resistance increases while drift velocity decreases?

    Thanks
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    (Original post by krisshP)
    MS
    http://www.scribd.com/mobile/doc/46124583?width=768
    QP
    http://www.scribd.com/mobile/doc/50654250?width=768

    I need help on question 18.

    With the first part why do you need a variable power supply/variable resistor?

    In cii why can't you say
    In I=nAvq the n value increases as there are more free electrons per metre cubed
    With I, A and q constant, drift velocity decreases??
    How do I know whether I am supposed to say this or say that there are more atomic vibrations, ausing more collisions between atoms and electrons, so resistance increases while drift velocity decreases?

    Thanks
    n will only increase if this is a thermistor - which it is not. The number of electrons free in the wire remains constant.
    You will need to know the bold in general, but what you said for a thermistor.
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    (Original post by joostan)
    n will only increase if this is a thermistor - which it is not. The number of electrons free in the wire remains constant.
    You will need to know the bold in general, but what you said for a thermistor.
    THANKS!
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    (Original post by krisshP)
    THANKS!
    Anytime
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    (Original post by joostan)
    Anytime
    Any ideas about why you need a variable power supply/variable resistor for the first part in the same question?
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    (Original post by krisshP)
    Any ideas about why you need a variable power supply/variable resistor for the first part in the same question?
    The mark scheme doesn't state that it MUST be a variable power supply/resistor. . .
 
 
 
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