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Homework Help: The Heating of Nichrome Wire in a toaster

  1. Sep 24, 2009 #1
    1. The problem statement, all variables and given/known data

    A toaster with a Nichrome heating element has a resistance of 70 ohms at 20oC and an initial current of 1.6 A. When the heating element reaches its final temperature, the current is 1.39 A. What is the final temperature of the heating element?

    2. Relevant equations


    3. The attempt at a solution
    I know that the voltage will remain constant therefore:
    I also know that Nichrome's [tex]\alpha[/tex]=100e-8
    but I don't really know where to go from here
  2. jcsd
  3. Sep 24, 2009 #2
    from [tex]

    \alpha = \frac {\rho - \rho_0} {\rho} (T_f - T_0)


    try to derive an equation for R as a function of R_0, T_0, T_f and [itex] \alpha [/itex]
    you know the new R from ohms law.

    The temperature coefficent of nichrome is [itex] 4 *10^{-4} K^{-1} [/itex]
  4. Sep 24, 2009 #3
    So am I going to be looking at resistivity then? such as [tex]\rho[/tex]=R*A/L ??
  5. Sep 24, 2009 #4
    yes. Instead of [tex]\rho[/tex]=R*A/L you can use [tex]\rho[/tex]=R*C. You don't know what A and L are anyway, except that they are constant.
  6. Sep 24, 2009 #5
    C as in capacitance? How do I find that?
  7. Sep 24, 2009 #6
    no it's just an arbitrary constant
  8. Sep 24, 2009 #7
    would that constant be in my physics book somewhere?
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