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: Copper resistance thermometer - temperature

  1. Jun 11, 2008 #1
    1. The problem statement, all variables and given/known data

    a piece of copper wire (rho_20 = 1.7*10^-8 ohm-m) is being used as a resistance thermometer.At 20 degrees celsius, the wire is known to have a resistance of 170 ohms. when the wire is immersed in a hot oil bath, its resistance increases to 173.4 ohms. if the temperature coefficient of resistivity is 10^-3, what is the temperature of the oil?

    assume that expansion of the copper negligible

    2. Relevant equations

    current density J = nqv_d where n is electron density, q is charge, v_d is drift velocity

    J = sigma*E where sigma is conductivity, E is electric field

    J = E/rho where rho is resistivity

    3. The attempt at a solution

    i really don't know where to start, is the 'temperature coefficient of resistivity' the same as rho?

    what equation do i use that relates temperature to resistance/rho? does it have anything to do with work, as work and heat have the same unit, joules?

    help appreciated..
  2. jcsd
  3. Jun 12, 2008 #2


    User Avatar
    Homework Helper

    is the 'temperature coefficient of resistivity' the same as rho?
    No. Go through any text book or Hyper Physics site. You will get the relation between the resistance of the conductor and change in temperature of the conductor.
    All your relevant equations are irrelevant!!
  4. Jun 12, 2008 #3
    okay found the equation:

    R = R_reference [1 + alpha(T - T_reference)]
    173.4 = 170( 1 + 10^-3(T - 20)]
    (173.4/170) - 1 + 0.02 = 10^-3T
    0.04/(10^-3) = T
    T = 40 degrees celsius

  5. Jun 12, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Looks good.

    FYI on units, the temperature coefficient of resistivity is 10^-3 per degree C,
    or 10^-3 / C.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook