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Homework Help: Weird equation on resistivity

  1. Jan 18, 2010 #1
    This is a suggested relationship between L/R and L

    L/R = kl + A/P

    P is the resistivity, A is the cross-sectional area and k is the constant for the circuit

    Using the value of the y-intercept find a value for P with the appropriate unit

    The graph of L/R against L had the intercept of 9 but I have no idea where that fits in. All I know is the answer must be in Ohms

    How do I calculate P?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 18, 2010 #2


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    L/R = kl + A/P

    is in the form Y=MX+C

    where C=A/p

    from a graph of Y vs X, how would you find C?
  4. Jan 18, 2010 #3


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    If the graph of L/R (y) against L (x) has an intercept of 9, you mean it crosses the y axis (where x=0) at 9
    Therefore 9 = 0 + A/P, so A/P is 9, from the intercept we don't have any info about the slope 'k'

    From this you can't separate resistivity and A - you could have a very narrow gold wire (low P) or a thick carbon (high P) one with the same resistance, ie the same P/A
  5. Jan 18, 2010 #4
    Yes it crosses the y axis at 9.
    Is k the gradient?

    I calculated A is 6.1 x 10⁻⁸ m² Is the equation possible now?
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