Stefan's law of radiation relates to which of the following?

Stefan's law (also called Stefan-Boltzmann law) is one of the most important laws in heat radiation. Option A is CORRECT — Stefan's law states that the total energy radiated per unit surface area of a black body per unit time (E) is directly proportional to the fourth power of the absolute temperature (T⁴). Mathematically: E ∝ T⁴ or E = σT⁴, where σ (sigma) is the Stefan-Boltzmann constant = 5.67 × 10⁻⁸ W/m²K⁴. This law was proposed by Josef Stefan in 1879 and derived theoretically by Ludwig Boltzmann in 1884. Option B is incorrect — the relationship is with T⁴ (fourth power), not T² (square). The square relationship does not correctly describe black body radiation. Option C is incorrect — the relationship between radiation wavelength and temperature is described by Wien's Displacement Law (λm × T = constant), not Stefan's law. Option D is incorrect — Stefan's law applies to an ideal black body and does not depend on the color of the body in the simple sense. A black body absorbs all radiation regardless of color.