A ball of surface temperature T is in thermal equilibrium with its environment. Which of the curve gives the energy E emitted by the sphere as a function of time 't'?

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TestHub · Accepted Answer

At thermal equilibrium the sphere remains at a fixed temperature.
$P_{emit} = ε σ A T^{4} = constant$
The graph asks for total energy emitted, not the emission rate.
$E (t) = \int_{0}^{t} P_{emit} d t = P_{emit} t$
Energy rises linearly with time from zero. Curve 2, answer B.

Physics - Heat & Thermo Question with Solution | TestHub

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