CAPE Physics Unit 1 · 2005 · Paper 2 · Question 8(b)(iii)

A home-made cooler is constructed from plywood and foam plastic. The walls consist of two pieces of plywood 1.0 cm thick with a 1 cm layer of foam plastic in between. When in use the temperature inside the box is 2 °C while the outside temperature is 30 °C. Figure VII shows a cross-section of the wall.

Using this equivalent thickness, or otherwise, find the rate of conduction of heat through a rectangular wall of the box which is 0.6 m by 0.4 m and deduce the temperatures at the two interfaces between plywood and plastic foam.