Researched
Planck's Quantum of Action
To explain heat radiation, Planck assumes (December 1900) that energy is exchanged in discrete packets E = hf.
Open in the interactive tree →Max Planck's radiation law matched measurements and introduced the constant h; Einstein used quanta of light to explain the photoelectric effect in 1905. The quantum of action is the start of quantum theory and, since 2019, helps define the kilogram.
Prerequisites
- Thermodynamics1824
- Electromagnetism1831-1865
- Statistical Mechanics1877
Unlocks
- Nucleus & Bohr Atom1911
- Quantum Mechanics1925Quantum mechanics grows from Planck's quantum of action
- Photovoltaics1954Solar cells rely on the photoelectric effect, explained with Planck's quanta
- Laser1960Einstein derived stimulated emission from Planck's radiation law