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Homework Help: Rate of heat flow

  1. Jan 7, 2009 #1
    1. The problem statement, all variables and given/known data

    Two rooms, each a cube 3.8 m on a side, share a 12 cm thick brick wall. Because of a number of 100 W light-bulbs in one room, the air is at 27°C, while in the other room it is at 10°C. How many of the 100 W light-bulbs are needed to maintain the temperature difference across the wall? (Round your answer up to the nearest integer.)

    2. Relevant equations


    3. The attempt at a solution

    This looks so easy and I attempt to solve it and I get it wrong.
    I used
    =(0.84J/s*m*C)(14.44m2)(27C-17C) / (0.12m)
    =1718.36 then divide by 100 and it equals 17.1836=17
    Do you have any ideas as to what I'm not comprehending because I'm sure this has to be the correct number of bulbs.
  2. jcsd
  3. Jan 7, 2009 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to PF :smile:

    The instructions say to round the answer up. Otherwise things look fine (assuming k is correct).
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