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Homework Help: Electric Resistance

  1. Feb 15, 2010 #1
    1. The problem statement, all variables and given/known data

    A 2.5 cm length of tungsten filament in a
    small lightbulb has a resistance of 0.041
    .
    Find its diameter. (The resistivity is
    5.6 × 10−8
    · m).
    Answer in units of mm.
    2. Relevant equations
    R=p(L/pi*r^2)


    3. The attempt at a solution
    i have reworked the equation to the square root of pL/R*pi equals r and then multiplied that answer by 2 which nds u being 2.0856e-4 but it is not right??
     
  2. jcsd
  3. Feb 16, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi bob12345! Welcome to PF! :smile:

    (have a pi: π and a rho: ρ and try using the X2 tag just above the Reply box :wink:)

    Method seems ok :smile:

    have you just got the decimal point in the wrong place before square-rooting?
     
  4. Feb 16, 2010 #3
    i didnt think so because i converted the length to meters..
     
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