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Homework Help: Diameter of tungsten wire

  1. Dec 28, 2011 #1
    1. The problem statement, all variables and given/known data

    If we know, that 200 mm of tungsten wire weight`s 1.72 mg, then what is the diameter of this wire

    2. Relevant equations

    3. The attempt at a solution

    I by my self came to the conclusion, that the answer is 0.13 mm. But if I take in accordance, that my Algebra and Physics is more than poor... may someone could calculate and prof this.

  2. jcsd
  3. Dec 28, 2011 #2
    "If we know, that 200 mm of tungsten wire weight`s 1.72 mg, then what is the diameter of this wire"

    Grams are mass, not weight.

    A wire is a long, thin cylinder. Compute volume in terms of diameter, then mass. Solve for diameter.
  4. Dec 28, 2011 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to Physics Forums.
    I calculate something different. If you show us your actual calculations, we can help figure out what went wrong.
  5. Dec 29, 2011 #4
    So I try`d to calculate it one more time this morning whis a fresh head and got some different:
    My Idea was to use formula for Desity, to get the Volume and then change the formula for cilinder volumen V=p*r2*h, for getting the radius

    200 mm = 0.2 m
    1.72mg= 0.00172 kg
    Denisty of tungsten = 19250 kg/m3

    1. Step. Density = Mass/Volume, so Volume = mass/density

    Volume = 0.00172/19250 = 0.000000008935 m3

    2. Step. V=p*r2*h; 0.000000008935=3.14*r2*0.2

    r=SQRT of 0.000000008935/3.14*0.20
    r= 0,0000238559904479939 m
    r=0.02385599 mm or the Diameter then would be 0.04771198 mm. This looks better...
    Last edited: Dec 29, 2011
  6. Dec 29, 2011 #5
    1.72mg= 0.00172 kg

    You are saying that 1.72 milligrams is 0.00172 kilogram???????
  7. Dec 29, 2011 #6
    0.000172 kg - one zero missed... everything else should be correct.
  8. Dec 29, 2011 #7
    Try again.
  9. Jan 1, 2012 #8


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    Staff: Mentor

    No - mg is not g. What does the 'm' stand for?
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