As a coffee enthusiast you wish to keep your coffee as hot as possible for as lo

Question

As a coffee enthusiast you wish to keep your coffee as hot as possible for as long as possible. You wish to find the rate of heat loss of a typical coffee mug. Assume the mug to be a cylinder which has a lid made out of the same material as the rest of the cylinder, and the thickness of the walls is 1.34 cm. If the coffee in the mug is 75.0 degree c and the room temperature is 20.0 degree c how much more heat does the mug lose through conduction than from radiated energy. See the hint below for important constants.

Explanation / Answer

Energy loss by radiation = emissivity * Stefan-Boltzmann Constant * ( T^4 - Ts^4)

Look under you hint button for the emissivity * Stefan-Boltzmann Constant * [(273+75.0)^4 - (273+24.0)^4]

= example 0.730 x 5.67x10^(-8) x [(273+75.0)^4 - (273+24.0)^4]

= 284.99W/m^2

Energy Loss = [0.850 W/m*C (75.0-24.0)C]/ 0.0134

= 3235.07

3235.07/284.99 =

=11.352 times

Note : under the Hint option in Sapling make sure its 0.850 W/m*C or adjust your numbers accordingly!!!

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