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Quantum nature of light

Physics (Year 12) - Wave Particle Duality and Quantum Theory

Dev Lohar

De Broglie wavelength

As we introduced in the interference notes, light has wave-particle duality. This means that light can behave as a wave (as seen in Young’s double slit experiment) in some situations, and as a particle (as seen in the photoelectric effect) in other situations. A physicist in 1924 by the name of Louis de Broglie proposed that if light can have particle-like properties, then maybe particles, or in general terms, matter, can have wave-like properties. He described the relationship between a particle and its wave property through an equation which states:

The de Broglie theory implies that any form of matter can behave like a wave and have a wavelength. An electron can also behave as a wave. This was observed in 1927 when the double slit experiment was conducted with electrons instead of light. Classically, we would imagine that only 2 bands would be observed on the screen behind the double slit, but an interference pattern was seen instead. The scientists were able to analyse the pattern to determine the wavelength of the electrons, and found that it was the same as the value theorised in the above equation.

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