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Homework Help: Resistivity of tungsten filament

  1. Mar 2, 2009 #1
    ]1. A 1.3 cm length of tungsten filament in a small lightbulb has a resistance of 0.032 ohms. Find its diameter.
    Given: Length= 1.3 cm= .013m
    R= 0.032 ohms
    resistivity= 5.6e-8 ohms*meter



    2.
    A= pi (r^2)
    R= resistivity (Length/ Area)



    3. The attempt at a solution
    R= resistivity ( Length/ pi* (r^2) )
    .032 ohms= (5.6e-8 ohms*meter) * (.o13m/ (pi* (r^2)) )
    .032 (pi) (r^2) = 7.28e-10
    .100530965 (r^2) = 7.28e-10
    r= 8.509e-5
    diameter= 2r= 1.701e-4m

    It asks for the answer in mm, so I divided my answer by 1000= 1.7 e-7 mm, but it's not correct = (
    What am I missing?
    Thanks in advance!
     
  2. jcsd
  3. Mar 2, 2009 #2
    1m=1000mm...
     
  4. Mar 2, 2009 #3
    wow do I feel silly! = / thanks
     
  5. Mar 2, 2009 #4
    Those things happen to everybody from time to time! :biggrin: And you're welcome!
     
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