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Finding the Specific Heat Capacity of a Potato

  1. Nov 30, 2014 #1
    1. The problem statement, all variables and given/known data
    So I've been trying to find the specific heat capacity of the potato for a while and keep coming up with an outrageous number (over 700,000 J/kgC)

    Here's what I've found

    mass of potato = 0.15kg
    initial T of potato = 18 degrees C
    final T of potato = 83 degrees C (is this not hot enough?)
    therefore change in T is 65 degrees C

    The power rating of my oven is 2000W, and I cooked it for 3600 seconds.

    2. Relevant equations
    I found the Q value by multiplying the oven's power by the time in seconds, so Q=7,200,000J

    I then used the equation c = Q/m∆T for the specific heat capacity

    3. The attempt at a solution

    c = 7200000/(0.15)(65) = 738462 J/(kg degrees C)

    We haven't done anything in my IB class about this subject, but I'm pretty sure that this number is way too big, and I can't figure out what to do, so I'm obviously missing something… Any suggestions? Thanks!
     
  2. jcsd
  3. Nov 30, 2014 #2

    haruspex

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    You're assuming all the energy went into heating the potato and stayed there.
    Start from the other end. Suppose the potato consists of water, which it mostly is. How long should you have to run the microwave for to get it to 100C? What will happen if you run it for longer?
     
  4. Dec 1, 2014 #3

    NascentOxygen

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    Hi Kendra. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    This is your own experiment? It might be better to start with a thoroughly heated potato and drop it into a jug of water and base your calculations on ΔT of that mass of water.
     
    Last edited by a moderator: May 7, 2017
  5. Dec 1, 2014 #4

    CWatters

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    Full marks for doing your own experiment but as haruspex pointed out not all the energy ends up in the potato. Ovens aren't very well insulated. Even quite good ones end up heating the whole kitchen sometimes.

    NascentOxygen suggests a way but I would cut the potato into small bits before heating otherwise when you put it into cold water it may take a long time to reach equilibrium and a lot of heat might escape while you wait. Perhaps use a thermos/vacuum flask instead of a jug of water?
     
  6. Dec 1, 2014 #5

    SteamKing

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    It's not clear what kind of oven the OP used to perform this experiment.

    If you cooked a potato for 1 hour(!) in a 2000 W microwave, is there anything left of the potato? Also, a microwave oven is not going to generate the same thermal radiation as a conventional oven will.

    Ditto, if the potato was cooked for 1 hour in an electric oven, how much was left, besides potato chips?
     
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