3.3.2.1
Historical development: from Newton's corpuscles to wave-particle duality
Interference & Diffraction — AQA A-Level Physics
- Newton (1672): proposed light is a stream of particles (corpuscles). Could not explain interference or diffraction.
- Huygens (1678): Wave Theory of Light. Each point on a wavefront acts as a source of secondary wavelets.
- Young (1801): double-slit experiment provided experimental proof that light is a wave.
- Maxwell (1862): showed light is electromagnetic waves (oscillating electric and magnetic fields perpendicular to each other).
- Einstein (1905): discovered the photoelectric effectThe emission of electrons from a metal surface when electromagnetic radiation of sufficiently high frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). is incident on it., showing light also behaves as particles (photons).
- This led to wave-particle dualityThe concept that all matter and radiation exhibit both wave-like and particle-like properties. Particles have a de Broglie wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m).; photons exhibit particle behaviour in the photoelectric effectThe emission of electrons from a metal surface when electromagnetic radiation of sufficiently high frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). is incident on it..: light behaves as both a wave and a particle.