Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?