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Homework Help: Specific Heat Capacity Graph Question

  1. Apr 12, 2016 #1
    1. The problem statement, all variables and given/known data
    My answer is question 3 part c the graph. SHC = c
    http://www.ocr.org.uk/Images/61757-question-paper-unit-g484-the-newtonian-world.pdf [See page 7]

    2. Relevant equations
    E=mcdelta theta Power=Energy/Time Therfroe
    Power*Time = Mass*c*delta theta.

    3. The attempt at a solution
    See in my coursebook similar question types have a horizontal line for when internal energy increases andpotential energy is constant.

    So my graph looks like a constant line, followed by a decreasing gradient followed by a constant line on the x axis horizontally foloweed by a line of decreasing gradient where the 2nd decreasing gradient line is less than the first.

    Essentially my shape is like a reclining chair if you can visualise this.

    However the mark scheme says this:

    1. 18 oC to 0 oC negative gradient line

    2. horizontal line on time axis

    3. 0oC to -18 oC line of steeper –ve gradient (judged by eye) than in 1

    The examiners report also says this:

    The most common error being ignoring the horizontal line during the change of state. Most candidates recognised that the line for the frozen milk needed to be steeper.

    From this would you say my graph is right or not as described above, they seem to omit the constant lines for when kinetic energy is constant.
  2. jcsd
  3. Apr 12, 2016 #2
    In my judgment, the book's answer is right and yours is wrong. I have no idea why your are referring to kinetic energy in this context. I also have no idea why you have a constant line to start with, unless you are referring to the time before the cooling begins. And I don't understand why you say that the gradient is decreasing, when the problem statements clearly says that heat is removed at a constant rate.
  4. Apr 13, 2016 #3
    Thank you for your reply. I figure it out. There was only one change of state from liquid to solid, hence one horizontal line to show this.

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