Physics

Problem

A composite wall has three layers in series, each of the same cross-sectional area. Their thicknesses and thermal conductivities are: Layer 1:

1\,\text{cm}

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

Layer 2:

2\,\text{cm}

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

Layer 3:

1\,\text{cm}

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

The inner surface is at

100^{\circ}\text{C}

and the outer surface at

20^{\circ}\text{C}

. The temperature at the interface between layers 1 and 2 (just after the first layer) is closest to a)

80^{\circ}\text{C}

88^{\circ}\text{C}

79^{\circ}\text{C}

56^{\circ}\text{C}