An oven with an inside temperature is in a room with a temperature of . There is a small opening of area in one side of the oven. We have to find the net power transferred from the oven to the room. We may consider both oven and room as cavities with .

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The total radiation power per unit area emitted from a cavity aperture is given by the Stefan-Boltzmann law, which states that

Temperature of the oven is ,

And the temperature of the room is .

As both oven and the room are assumed to be cavities with emissivity , the net power transferred to the room per unit time from the hole in the oven of area will be