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Homework Help: Find the time needed to warm the water to a temperature

  1. May 23, 2015 #1
    1. The problem statement, all variables and given/known data
    An electrical resistence has a power of 1 kW. It is put inside a container that has 10 liters water. The water is in temperature 20C with pressure 1 atm. Find the time to warm the water to the temperature 120C

    2. Relevant equations

    3. The attempt at a solution
    I thought to use the equation p1/T1=p2/T2 and t=P/A. How can i find A?
  2. jcsd
  3. May 23, 2015 #2


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    Hello MB,

    Well, if A is P*t, then writing t = P/A seems a little strange !

    So perhaps you can shed a little light here ? First of all, what are these symbols representing ? And their dimensions ?

    Warming up water takes heat, energy. The more energy per unit of time (a.k.a. power), the faster it goes.

    Furthermore, they tell you the 10 liters of water are at a temperature of 20 ##^\circ##C in a container at a pressure of 1 atm. They don't tell you if the container is closed and kept at a constant volume, or if it's open. In other words, what happens at a temperature of, say, 100 ##^\circ##C :rolleyes: ?

    [edit]Oh, and your thread will soon be moved to the introductory physics section by the good spirits that watch over PF
    Last edited: May 23, 2015
  4. May 24, 2015 #3
    I corrected it. t-time, A-work, P-power
  5. May 24, 2015 #4


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    Good (although I don't see it anywhere).
    What about the p1T1 = p2T2 ? what are they ?
    Can you write an equation to calculate how much energy is needed to heat up 10 liters of water by one degree C ?
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