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Thermal Radiation. Quantum Nature of Light.

Problem 5.251

A copper ball of diameter d=1.2 cmd=1.2 \mathrm{~cm} was placed in an evacuated vessel whose walls are kept at the absolute zero temperature. The initial temperature of the ball is T0=300 KT_{0}=300 \mathrm{~K}. Assuming the surface of the ball to be absolutely black, find how soon its temperature decreases η=2.0\eta=2.0 times.

Reveal Answer
t=(η3−1)cod⁡/18σT03=3 hours, where c is the specific heat capacity of copper, p is its density. t=\left(\eta^{3}-1\right) \operatorname{cod} / 18 \sigma T_{0}^{3}=3 \text { hours, where } c \text { is the specific heat capacity of copper, p is its density. }
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