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Homework Help: Change in entropy of a resistor

  1. Oct 2, 2016 #1
    1. The problem statement, all variables and given/known data
    Consider a thermally insulated resistor with resistance R=20 Ω and mass m=5.0 g. The resistor is made of a material with specific heat capacity c=850 J/(g-K) and carries a current of 2.0 A for a time period of 1.0 s.

    a) Calculate the increase in the temperature of the resistor if it has initial temperature Tin=20oC. Recall that the power dissipated by a resistor is given by P=I²R.

    b) Determine the increase in the resistor's entropy over the period that the current passes through it.

    2. Relevant equations

    3. The attempt at a solution
    My solution is in the attachment. I just wanted somebody to have a look at it and let me know if it looks okay since I don't feel too sure about it.

    Attached Files:

  2. jcsd
  3. Oct 2, 2016 #2


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    Staff: Mentor

    I note that you used 50g for your mass in the final calculation rather than 5g...
  4. Oct 2, 2016 #3
    oh woops, the answer should have been ΔS = 0.273 J/K
  5. Oct 3, 2016 #4

    rude man

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    Homework Helper
    Gold Member

    I think part (b) is a trick question but I'm going to wait for other responses if any.
    As a hint I don't agree with the computed answer in post 3.
  6. Jan 11, 2017 #5
    Your specific heat capacity is unrealistic. It should be per kilo not gram.
  7. Jan 13, 2017 #6
    Yes, the approach is correct, but the heat capacity is off by a factor of 1000.
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