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Homework Help: Fuse wires

  1. Feb 8, 2007 #1
    1. The problem statement, all variables and given/known data

    does the length of the fuse wire influence its cpacity? why?

    2. Relevant equations

    R=pL/a

    3. The attempt at a solution
    My teacher said no. I think it should because R depends on L


    Thanks for your time.
     
  2. jcsd
  3. Feb 8, 2007 #2

    Andrew Mason

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    Homework Helper

    I think I would agree with your teacher. The fuse capacity (the largest current permitted to flow) depends on the temperature of the fuse wire. At a certain temperature, it melts and stops the current. Off hand, I would say that the temperature depends upon the power density being dissipated in the fuse wire (power / unit volume). The power dissipated is [itex]I^2R = I^2\rho L/A [/itex]

    Now, the power per unit volume is:

    [tex]P/Vol = P/LA = I^2\rho L/A(LA) = I^2\rho/A^2[/tex]

    So it appears to me that the L falls out and the temperature depends entirely upon the cross sectional area of the fuse wire.

    AM
     
  4. Feb 8, 2007 #3
    Thanks. I think your answer makes sense.
     
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