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Homework Help: Diameter of wire from voltage, length, resistivity

  1. Mar 15, 2010 #1
    1. A standard 100 W (120 V) lightbulb contains a 8.50 cm-long tungsten filament. The high-temperature resistivity of tungsten is 9.0*10^{ - 7} ohm*m. What is the diameter of the filament?

    2. p= resistivity, E = V/L, I = AV/pL, R = pL/A...

    3. I know that I'm going to solve for A = pi*r2, find r and multiply by 2 to get the diameter, but I just don't see how to do it with what I'm given. For example, I could do pi*r2 = IpL/V but I don't know I, or A = pL/R but I don't know R....
  2. jcsd
  3. Mar 15, 2010 #2
    The information that the bulb operates at 100W and 120V allows you to calculate the current through it and its resistance. Do you know a formula relating power to voltage and current?
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