Wien's displacement lawlaw

Imagine you are heating a piece of metal. At first it’s dark, then red, then yellow, and even blue. Wien's displacement law explains how the color of the glow depends on temperature: the hotter the body, the shorter (bluer) the waves it emits. It is as if you move a color slider on a screen: more heat — go to blue, less — to red. The formula is simple: λ_max × T = constant, where λ_max is the wavelength at which most light is emitted, and T is the temperature in Kelvin.

Discovered in 1893 by Wilhelm Wien, the displacement law describes the peak radiation of a black body. Historically, it was an important step toward understanding the quantum nature of light. Analogy: imagine a large orchestra where each musician plays a note (wavelength). The 'hotter' (faster) the conductor sets the tempo, the higher the notes on average. Wien found that all 'notes' do not sound equally loud — there is a loudest note, and its pitch is inversely proportional to the tempo. Similarly, a body does not radiate all wavelengths equally: there is a wavelength at which intensity peaks, and it shifts inversely with temperature.

Wien's displacement law is a physical law establishing the dependence of the wavelength at which the spectral energy density of a black body's radiation reaches a maximum on temperature. Strictly: λ_max = b / T, where b ≈ 2.898×10⁻³ m·K. The law was derived by Wilhelm Wien in 1893 as a consequence of thermodynamics and electromagnetism, before the creation of quantum theory. It later became important evidence for the need for a quantum hypothesis, since classical physics could not explain why the peak shifts toward shorter wavelengths with increasing temperature.