What are the 4 laws of radiation?

The four laws of radiation are Planck’s Law, Stefan-Boltzmann Law, Wien’s Displacement Law, and Kirchhoff’s Law. These laws explain how objects emit and absorb radiant energy (heat and light).

1. Planck’s Law

This law explains the amount of radiation emitted by a black body at a specific temperature and wavelength. It shows that radiation increases with temperature and changes with wavelength.

• Higher temperatures emit more radiation.
• Radiation is not the same for all wavelengths—it peaks at certain points depending on temperature.

2. Stefan-Boltzmann Law

This law states that the total energy radiated by a black body is proportional to the fourth power of its absolute temperature (T⁴).

Formula: E = σT⁴

• E is the energy emitted per unit area.
• σ (sigma) is the Stefan-Boltzmann constant.

This means if temperature doubles, the radiation increases by 16 times!

3. Wien’s Displacement Law

This law tells us the wavelength at which maximum radiation is emitted by a black body. As temperature increases, the peak of radiation moves to shorter wavelengths.

Formula: λ_max × T = constant

• Hotter objects emit radiation at shorter wavelengths (e.g., blue light).
• Cooler objects emit at longer wavelengths (e.g., red light or infrared).

4. Kirchhoff’s Law

This law says that a good absorber of radiation is also a good emitter. A black body, which absorbs all radiation, also emits the maximum possible radiation at a given temperature.

For any body: Emissivity = Absorptivity