A 25 watt light bulb is placed in a 10 in x 10 in acrylic box with sides and a bottom that are 3/16 inches thick and are fantastic insulators. The heat lost from the sides and bottom of this box is so small, you can assume it is 0. A 1/2-inch thick cover (10 in x 10 in) made of unknown material is placed on top of the box where heat can escape more readily. When the light bulb is on, the temperature inside the box is 10 degrees higher (in celsius) than it is on the outside.
Determine the thermal conductivity (k) for the unknown insulating material. Remember to convert inches to meters!!
W/m*K (Precision of 0.00)
If 10 minutes go by, how many joules of energy (Q) has the lightbulb given off inside the box?
(Precision of 1000)
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Answer:
Heat flows in the opposite direction to the temperature gradient. The ratio of the rate of heat flow per unit area to the negative of the temperature gradient is called the thermal conductivity of the material: dQdt=−KAdTdx.
There are several methods of experimentally determining thermal conductivity, such as the steady state or comparative method, the radial flow method, the laser-flash diffusivity method, and the pulse-power method [1].
Explanation:
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