Stefan-Boltzmann Law (H = Aeσ T⁴ ; Hnet = Aeσ(T⁴ − Ts⁴))
jee-mainjee-advancedneet-ug
H = Aeσ T⁴ ; Hnet = Aeσ(T⁴ − Ts⁴)
What each symbol means
| Symbol | What it stands for |
|---|---|
| A | Surface area of the body (m²) |
| H | Total power radiated by the body (W) |
| T | Absolute temperature of the body (K) |
| e | Emissivity of the surface (0 ≤ e ≤ 1, dimensionless) |
| Ts | Absolute temperature of the surroundings (K) |
| σ | Stefan-Boltzmann constant = 5.67 × 10⁻⁸ W m⁻² K⁻⁴ |
| Hnet | Net rate of heat loss by radiation (W) |
When to use this
For a perfect blackbody, e = 1. For real bodies, e < 1 (e.g., tungsten lamp e ≈ 0.4, human skin e ≈ 0.97). Power radiated ∝ T⁴ — very sensitive to temperature. Net radiation considers both emission and absorption from surroundings. Blackbody radiation curves are universal — depend only on T.