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Specific Heat Capacity of a brass cylinder

  1. Mar 17, 2007 #1

    The temperature of a brass cylinder of mass 100g was raised to 100 degree celsius and then transferred to a thin aluminium can of negligible heat capacity. The aluminium can contained 150g of paraffin at 11 degree celcius. If the final steady temperature after stirring was 20 degree celsius, claculate the specific heat capacity of paraffin

    (Neglect heat losses, and assume specific heat capacity of brass= 38 J/gK

    2. Relevant equations

    Specific heat capacity * mass * change in temperature = Energy lost/gained

    3. The attempt at a solution

    The answer given by my teacher is: 2250J/Kg.K

    My answer and workings:

    100 * 28 * 80 = 150 * 9 * Specific heat capacity of paraffin

    Specific Heat Capacity = 225 J/g.K

    Even if I change this value to J/kg.K (which I don't know how to), I won't get the answer my teacher gave- that much I can tell :-(

    Someone I asked gave the correct answer, but they didn't take the weight of the cylinder into account. Why is this possible?
    Last edited: Mar 17, 2007
  2. jcsd
  3. Mar 17, 2007 #2


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    Homework Helper

    Based on the numbers in your question, I get the same answer as you. I think problem is with the specific heat capacity of brass. I think it should be 0.38 J/gK (I looked it up). Using that value will give you the same answer as your teacher if you convert it to J/kgK. Are you sure you copied it down right?

    Well, I can't see how they got the right answer by doing that, why would they leave out the mass of the cylinder only? Did they still include the mass of the paraffin? I think it might just be coincidence that it came out to the right answer. But I don't think the units would match that of your teacher's answer (so technically it would be wrong). I'm just guessing since I don't know what they really did.
  4. Mar 18, 2007 #3
    Thank you sooo much! So my method is right then. That's all I wanted to know. :-D

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