Laws of Blackbody Radiation
Blackbody Radiation Graph
Blackbody Radiation Examples
1. Planck’s Law
Planck’s law gives the amount of radiation emitted per unit solid angle in terms of wavelength or frequency and equilibrium temperature. According to Planck’s law, the spectral radiance at a given temperature is given by Where B: Spectral radiance λ: Wavelength of radiation T: Absolute temperature c: Speed of light h: Planck’s constant
2. Wien’s Law or Wien’s Displacement Law
Wien’s law states that the wavelength at which a blackbody emits radiation with maximum intensity is inversely proportional to the absolute temperature. Where λmax: Wavelength at which the radiation intensity is maximum, known as peak wavelength b: A constant called Wien’s constant, whose value is 2.897 x 10-3 m·K T: Absolute temperature
3. Stefan-Boltzmann’s Law
Stefan-Boltzmann’s law states that the total radiant power emitted by a surface across all wavelengths is proportional to the fourth power of its absolute temperature. Therefore, the total energy radiated by a blackbody depends on its temperature. P: Radiant power A: Surface area T: Absolute temperature These curves have the following features:
- The shape of the curve is continuous and complex, as described by Planck’s law.
- Each curve passes through a maximum corresponding to its peak wavelength.
- The peak wavelength decreases with temperature, as stated by Wien’s law.
- The intensity of radiation increases as the temperature increases.
- The total radiated energy (the area under the curves) increases rapidly as the temperature increases, a consequence of Stefan-Boltzmann’s law.
- All blackbodies above absolute zero temperature emit radiation, although the intensities are low at short and long wavelengths.
