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Finding diameter of a wire based on the current and current density.

  1. Oct 17, 2006 #1
    You need to design a 0.9 A fuse that "blows" if the current exceeds 0.9 A. The fuse material in your stockroom melts at a current density of 540 A/cm2. What diameter wire of this material will do the job?

    540x10^-2=5.40 A/m^2

    5.40= .9/x

    Solving for x gives the answer: .166666666666667

    Then:

    .166666666667=pi(r^2)

    sqrt(.166666666667/pi)=r

    The result of that answer multiplied by 2 gives 4.607m. The answer asks for it in mm so I converted to 460.7mm and it says its wrong. Where did I go wrong, I'm just using the current density formula: J=I/A

    Where J is the current density
    I is the current
    A is the area
     
  2. jcsd
  3. Oct 18, 2006 #2

    OlderDan

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    Science Advisor
    Homework Helper

    Do what you did again, only this time keep track of your units every step along the way. Unit consistency will do wonders for you.
     
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