Wave-Particle Duality
Double-slit with wave, particle, and both modes — see interference fringes build from discrete hits.
Key Notes
Wave-particle duality: light and matter both exhibit wave-like AND particle-like properties depending on the experiment.
Light: behaves as wave in interference, diffraction, polarisation. Behaves as particle (photon) in photoelectric effect, Compton scattering, pair production.
Matter: behaves as particle in collision/Newtonian experiments. Behaves as wave in electron diffraction (Davisson-Germer, 1927), neutron interferometry, etc.
The two pictures are COMPLEMENTARY — you can't see both at once. Bohr's complementarity principle.
Photon energy E = hf, momentum p = h/λ. Matter wavelength λ_dB = h/p (de Broglie).
For everyday objects (e.g., a thrown ball), de Broglie wavelength is fantastically tiny (~10⁻³⁴ m) — wave nature is undetectable.
Wave-particle duality is a foundational pillar of quantum mechanics — it eventually led to the Schrödinger equation, where particles are described by wavefunctions.
Formulas
Photon (light as particle)
Particle properties: discrete energy and momentum.
de Broglie (matter as wave)
Wave properties: every moving particle has an associated wavelength.
Energy-momentum relation (massive)
Relativistic — important for fast electrons.
Important Points
Wave and particle pictures are not contradictory — they describe DIFFERENT EXPERIMENTAL OUTCOMES.
Same experiment cannot show both pictures simultaneously (e.g., 'which-slit' detection destroys interference).
For massive objects, λ_dB = h/(mv) is extremely small ⇒ classical (particle) behaviour dominates.
For electrons at typical accelerating voltages (50–100 V), λ_dB ~ 0.1 nm — comparable to atomic spacing ⇒ diffraction observable.
Double-slit experiments with single photons / electrons show interference builds up dot-by-dot — proving wave + particle simultaneity.
All matter has wave nature; the question is whether λ_dB is large enough to detect.
Wave-Particle Duality notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.