• id: JME-10-N13
• title: Thermal Radiation and Stefan-Boltzmann Law
• tags: radiation, stefan-boltzmann, blackbody

All bodies above 0 K emit thermal radiation. A blackbody is a perfect absorber and emitter. Stefan-Boltzmann law: $P = \sigma AT^4$ (blackbody), $P = e\sigma AT^4$ (real body with emissivity $e$, $0 \leq e \leq 1$). The net power radiated in surroundings at temperature $T_s$: $P_{\text{net}} = e\sigma A(T^4 - T_s^4)$. Key: radiation depends on $T^4$, so small temperature changes produce large power changes. Doubling absolute temperature increases radiation by 16 times. Good absorbers are good emitters (Kirchhoff's law): $e = a$ (absorptivity) at thermal equilibrium.