Which form of energy emission is described by Stefan-Boltzmann law as proportional to T^4?

• A. Planck's law
• B. Wien's law
• C. Stefan-Boltzmann Law
• D. Kirchhoff's law

Answer: (C)

The main concept here is how total radiant energy emission from a body depends on temperature. The Stefan-Boltzmann law says that the total power radiated per unit area by a blackbody is proportional to the fourth power of its absolute temperature: P/A = sigma T^4. This result comes from integrating Planck’s law over all wavelengths to get the overall energy output, not just at a particular wavelength. The Stefan-Boltzmann constant sigma is about 5.67 × 10^-8 W·m^-2·K^-4. For real surfaces, the emitted power is epsilon sigma T^4, where epsilon is the emissivity between 0 and 1. In contrast, Planck’s law describes the spectral distribution of emission at a given temperature, Wien’s law gives where that emission peaks in wavelength, and Kirchhoff’s law relates emissivity to absorptivity at thermal equilibrium.