1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    p=resistivity
    P=power
    L=length of wire
    A=cross sectional area of wire
    I=Current
    V=Voltage

    R=pL/A
    R=V/I
    P=IV

    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

    tiny-tim

    User Avatar
    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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Resistance and Resistivity problem
  1. Resistance problem (Replies: 1)

  2. Resistivity Problem (Replies: 8)

  3. Resistance problem (Replies: 1)

Loading...