• Tags: planck, quantum, black-body
• Difficulty: Foundation

Max Planck (1900) proposed that electromagnetic radiation is emitted and absorbed in discrete packets called quanta. The energy of each quantum is E = hf, where h = $6.626 \times 10^{-34} J·s is Planck's constant and f is the frequency. This resolved the ultraviolet catastrophe — classical theory (Rayleigh-Jeans law) predicted infinite energy at short wavelengths for black-body radiation, while Planck's formula gave finite energy that matched experiments perfectly. The quantum hypothesis was revolutionary: it introduced the concept of energy quantization for the first time, breaking from the classical continuous energy assumption. Wien's displacement law (λ_max × T = \2.898 \times 10^{-3}$m·K) and Stefan's law (P = σ$AT^{4}$) remain valid and are derived from Planck's distribution.