Homework Help: Change in entropy of a resistor

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1. Oct 2, 2016

Elvis 123456789

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.

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2. Oct 2, 2016

Staff: Mentor

I note that you used 50g for your mass in the final calculation rather than 5g...

3. Oct 2, 2016

Elvis 123456789

oh woops, the answer should have been ΔS = 0.273 J/K

4. Oct 3, 2016

rude man

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.

5. Jan 11, 2017

alchemistoff

Your specific heat capacity is unrealistic. It should be per kilo not gram.

6. Jan 13, 2017

Staff: Mentor

Yes, the approach is correct, but the heat capacity is off by a factor of 1000.