Calculate Heat Flow Rate Across a Wall: 100 W Lightbulbs

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SUMMARY

The discussion centers on calculating the heat flow rate across a brick wall separating two rooms with different temperatures due to 100 W lightbulbs. The equation used is Q/t = kA(t1-t2)/l, where k is the thermal conductivity, A is the area, t1 and t2 are the temperatures, and l is the thickness of the wall. The user initially calculated the required number of bulbs to maintain the temperature difference but arrived at an incorrect conclusion. The correct approach involves ensuring the final answer is rounded up as per the problem's instructions.

PREREQUISITES
  • Understanding of heat transfer principles, specifically conduction.
  • Familiarity with the equation Q/t = kA(t1-t2)/l.
  • Knowledge of thermal conductivity values, such as k = 0.84 J/s*m°C for brick.
  • Basic algebra skills for manipulating equations and rounding numbers.
NEXT STEPS
  • Review the concept of thermal conductivity and its applications in building materials.
  • Learn about the implications of temperature differences in heat transfer scenarios.
  • Practice solving similar heat transfer problems using the Q/t equation.
  • Explore the effects of insulation thickness on heat flow rates in walls.
USEFUL FOR

Students studying thermodynamics, physics enthusiasts, and anyone involved in building design or energy efficiency assessments.

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Homework Statement



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.)

Homework Equations



Q/t=kA(t1-t2)/l

The Attempt at a Solution



This looks so easy and I attempt to solve it and I get it wrong.
I used
Q/t=kA(t1-t2)/l
=(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.
 
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Welcome to PF :smile:

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

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