A cottage wall of area is built in three layers placed one after another along the…

PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

A cottage wall of area

2.5\,\text{m}^2

is built in three layers placed one after another along the direction of heat flow: Layer 1 (plaster): thickness

1\,\text{cm}

k = 0.90\,\text{W m}^{-1}\,\text{K}^{-1}

Layer 2 (glass wool): thickness

5\,\text{cm}

k = 0.04\,\text{W m}^{-1}\,\text{K}^{-1}

Layer 3 (plywood): thickness

1\,\text{cm}

k = 0.12\,\text{W m}^{-1}\,\text{K}^{-1}

The room is kept at

25^{\circ}\text{C}

and the outside temperature is

5^{\circ}\text{C}

. (i) Show that the equivalent thermal conductivity of the composite wall is nearly

0.05\,\text{W m}^{-1}\,\text{K}^{-1}

. (ii) Using the value obtained in part (i), compute the steady rate of heat loss through the wall.