A box with a total surface area of 1.47 m2 and a wall thickness of 3.91 cm is made of an insulating material. A 15.9 W electric heater inside the box maintains the inside temperature at 8.4 ◦C above the outside temperature. Find the thermal conductivity of the insulating material. Answer in units of W/m · ◦ C.

0.05 W/m°C

Explanation:

Surface area of box, A = 1.47 m²

thickness of wall, d = 3.91 cm = 0.0391 m

Power of heater, P = 15.9 W

difference in temperature, ΔT = 8.4 °C

Let K is the thermal conductivity.

Heat flows per unit time is given by

K = 0.05 W/m°C

Thus, the thermal conductivity of the box is 0.05 W/m°C.

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