In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. It is defined as the quantity of heat, *Q*, transmitted in time *t* through a thickness *L*, in a direction normal to a surface of area *A*, due to a temperature difference Δ*T*, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.

thermal conductivity = heat flow rate × distance / (area × temperature difference)

**Try the following problems, using the above equation. **

The drawing shows a composite slab consisting of three materials through which heat is conducted from left to right. The materials have identical thicknesses and cross-sectional areas. Rank the materials according to their thermal conductivities, largest first.

- (Answer: k3, k2, k1)

Heat is conducted through the two slabs shown in the drawing. The slabs have identical thicknesses and cross-sectional areas, but they are made from different materials. The thermal conductivity of slab 1 is *k* _{1} = 85 J/(s · m · C ° ). What is the thermal conductivity *k* _{2} of slab 2? Give your answer to two significant figures, e.g., 45 J/(s · m · C °).

- (Answer: 170smC)

A can of gasoline has a rectangular base with dimensions of 13.5 cm by 13 cm. If there are 3 liters of gasoline in the can, how much does the surface of the gasoline rise (in mm) in the can when the temperature is raised by 45^{o}C? The coefficient for volume expansion of gasoline is 9.5 x 10^{-4}/^{o}C.

- (Answer: 7.29mm)

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