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# PLANCK'S LAW - Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. - It is a fundamental concept in quantum mechanics. ## EQUATION $B(v,T) = \frac{2hv^3}{c^2} \frac{1}{e^{\frac{hv}{kT}}-1}$ Where: - B...

# PLANCK'S LAW - Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T. - It is a fundamental concept in quantum mechanics. ## EQUATION $B(v,T) = \frac{2hv^3}{c^2} \frac{1}{e^{\frac{hv}{kT}}-1}$ Where: - B is the spectral radiance (the power emitted per unit area, per unit solid angle, per unit frequency). - $v$ is the frequency of the electromagnetic radiation. - T is the absolute temperature of the black body. - $c$ is the speed of light in a vacuum. - $h$ is Planck's constant. - $k$ is Boltzmann's constant. ### Key Points - The law shows that the amount of energy radiated by a black body is not continuous but is emitted in discrete packets or quanta. - As the temperature increases, the total amount of radiation increases, and the peak of the spectrum shifts to shorter wavelengths. - Planck's law accurately describes the black body radiation spectrum and resolves the ultraviolet catastrophe predicted by classical physics. ## Plot of Planck's Law - The two axes are Wavelength and Spectral Radiance. - There are 3 plots on the same graph, each representing a temperature: 4000K, 5000K and 6000K. - Each plot shows how Spectral Radiance reaches a maximum at a certain wavelength, before dropping. - The maximum Spectral Radiance increases with temperature and also occurs at a lower wavelength.