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I have got a problem here:I was given this:A 125W heater and

  1. Mar 6, 2004 #1
    I have got a problem here:

    I was given this:

    A 125W heater and a thermometer are immersed in 0.6kg of oil in a vessel of negligible heat capacity. The following results were obtained.

    Temperature (K) 294 302 313 324 334
    Time (minutes) 2 4 6 8 10

    How would you find the time at which heating started?

    would it be the x value when y = 0, but x (time) would be negative.

    Can someone help? Thank you.

  2. jcsd
  3. Mar 6, 2004 #2


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    What do you mean by "started heating"? You would need to know an inital temperature. Without that the question is pretty meaningless.
  4. Mar 8, 2004 #3
    the information I posted above is all the information I have on the question.......
  5. Mar 8, 2004 #4


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    The only interpetation of that problem that makes any sense is that the heaters were turned on at t=0. Thus heating started at t=0
  6. Mar 9, 2004 #5
    I don't believe there is enough info given.
    Most likely it is a typo and the requirement is actually the starting temperature.
    In this case a way to do it would be:

    An energy balance on the oil,

    m.Cp.[T - T0] = q.t

    (assuming heating starts at t=0)


    T(t) = (q/m/Cp)t + T0

    Take the data & plot. Should be straight line of intercept T0.

    p.s. There's nothing wrong with time being negative, it's all relative to where zero is defined.
    However a temperature of zero kelvin is highly unlikely, i.e. your oil would probably be a frozen rock.
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