Detailed Summary
This section delves into the particle nature of electromagnetic radiation, as articulated in Planck’s Quantum Theory. Classical physics struggled to explain several experimental observations, including the behavior of black-body radiation, the photoelectric effect, the variation in solid heat capacity with temperature, and the line spectra of atoms. Notably, Planck’s 1900 work highlighted that energy is quantized—meaning systems can only absorb or emit discrete energy amounts (quanta).
Planck introduced the concept of the black body, an idealized object that perfectly absorbs and emits radiation, with properties profoundly influenced by temperature. His famous equation, E = hν, denotes that the energy of a quantum is proportional to its frequency, where h is Planck’s constant.
The section further discusses the photoelectric effect, experimentally observed by Hertz, wherein electrons are emitted from a metal surface when exposed to light of sufficient frequency. This phenomenon contradicts classical physics expectations, as energy transfer is instant, and energy ejection depends on frequency, not intensity. Einstein later applied Planck’s theory to explain these observations, affirming the dual wave-particle nature of light, which remains crucial for understanding modern physics.