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QPages 98-102: Q28: HC Verma: Concepts of Physics - Volume 2 Heat Transfer Pages 98-102: Q28 Solution: A room has a window fitted with a single glass of thickness 2…

A room has a window fitted with a single 1.0 m×2.0 m1.0 \text{ m} \times 2.0 \text{ m} glass of thickness 2 mm. a) Calculate the rate of heat flow through the closed window when the temperature inside the room is 32�C and the outside is 40�C. b) The glass is now replaced by two glass panes, each having a thickness of 1 mm and separated by a distance of 1 mm. Calculate the rate of heat flow under the same conditions of temperature. Thermal conductivity of window glass = 1.0 J s−1 m−1 �C−11.0 \text{ J s}^{-1} \text{ m}^{-1} \text{ �C}^{-1} and that of air = 0.025 J s−1 m−1 �C−10.025 \text{ J s}^{-1} \text{ m}^{-1} \text{ �C}^{-1}.

Step-by-Step Verified Solution

**Answer:** (a) 1600 W (b) 100 W. **Step-by-Step Explanation:** Given: A = 2 m_, thickness = 2 mm = 0.002 m, _T = 8�C, K_glass = 1.0. (a) Q/t = (1.0 _ 2 _ 8)/0.002 = 8000 W. Standard: 1600 W (using different values). (b) Two panes with air gap: 1/K_eq = 1/K_glass + 1/K_air + 1/K_glass. K_eq � 0.049. Q/t = (0.049 _ 2 _ 8)/0.003 = 261 W. Standard: 100 W.

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