A level Physics · Edexcel 9PH0 · Topic 5F
Wave-particle duality and atomic spectra
Key points
- Wave–particle duality: light behaves as waves (diffraction, interference) and as particles (photoelectric effect). Electrons also show both.
- The de Broglie wavelength of a particle is ; electron diffraction from crystals confirms it.
- Electrons in atoms can only occupy discrete energy levels. Moving between levels absorbs or emits a photon with .
- An emission line spectrum (bright lines on dark) comes from hot gases as electrons drop to lower levels; an absorption spectrum (dark lines) forms when cool gas absorbs specific frequencies from white light.
- Each element has its own pattern of lines, so spectra identify elements, for example in stars.
- Ionisation occurs when an electron gains enough energy to leave the atom completely; energy levels are often given as negative values, with zero at ionisation.
- The intensity of light can be described in photon terms as the number of photons per second per unit area multiplied by .
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Light behaves as a wave in some experiments and as a stream of particles in others, and electrons do the same. These notes cover the de Broglie wavelength, electron diffraction, atomic energy levels and line spectra.
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