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Homework Help: Resistance and Resistivity problem

  1. Mar 29, 2009 #1
    1. The problem statement, all variables and given/known data

    A piece of Nichrome wire has a radius of 8.6 x 10^-3 m. It is used in a laboratory to make a heater that dissipates 575 W of power when connected to a voltage source of 120 V. Ignoring the effect of temperature on resistance, estimate the necessary length of wire.

    Nichrome wire had resistivity of 100x10^-8

    2. Relevant equations

    L=length of wire
    A=cross sectional area of wire


    3. The attempt at a solution

    I first solved for current, since i'd need to plug resistance into the first equation to make L the only unknown. So P/V=I gives I=4.792 Amperes. Then I needed to take the radius of the wire and make it into cross sectional area, so A=(pi)r^2.......A=.000232 m^2.

    Now to solve the first equation for L.....L=pV/IA.

    L=(100x10^-8 ohm-m)(120 V)/(4.792 A)(.000232 m^2)

    now, i know i'm getting the wrong answer of .1079 m. can anyone tell me what i'm doing wrong?
  2. jcsd
  3. Mar 29, 2009 #2


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    Science Advisor
    Homework Helper

    Hi Snowman2526! :wink:

    (have a rho: ρ :wink:)
    Noooo … ρ = (A/L)(V/I), so L = … ? :smile:
  4. Mar 30, 2009 #3
    thank you sir :) problem solved
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