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!

Homework Help: The Rate at which kinetic energy changes to thermal energy

  1. Apr 14, 2013 #1
    A potential difference of 50 mV is maintained between the ends of a 9.70 m length of wire whose cross section area is 25.0mm^2. The conductivity of the wire is 6.80 x 10^6 (ohm.m)^-1. Determine the rate at which the energy in the wire is transformed into kinetic to thermal energy.

    2. Relevant equations
    P = v^2/R

    ρ = 1/c

    R = ρ (L/A)

    Where ρ = resistivity
    c = conductivity
    A = area
    L = length
    R = Resistance
    V = Voltage
    P = power

    3. The attempt at a solution

    ρ = 1/6.80 x 10^6 = 1.471 x 10^(-7)

    R = 1.471 x 10^(-7) * ( 9.70/0.000025 )
    = 0.0570748
    P = (50 x 10^-3)/0.0570748
    = 0.0438021
    = 4.38 x 10^(-2) W

    This is my complete work. I think my workings are correct but My instructor says my answer is wrong. I will be glad if anyone can help.
  2. jcsd
  3. Apr 14, 2013 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Where do you have kinetic energy? I think this should be electric energy.

    There is a ^2 missing at P=, but the following line is correct. Units are missing everywhere :(.
    I would express the final answer in mW or W. I agree with the result, however.
  4. Apr 14, 2013 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    This is a duplicate of post https://www.physicsforums.com/showthread.php?t=685309, 1 hour earlier, apparently just to change the title.
    As mfb says, there's is no kinetic energy involved here, unless you mean thermal energy viewed as kinetic at the atomic level.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted