Waves and Light: Wave-Particle Duality

Wave-Particle Duality of Light

Key Concepts:

Wave-Particle Duality refers to the concept that all particles exhibit both wave and particle properties. This principle is a fundamental aspect of quantum mechanics.
Light is a perfect example of this duality; it can behave as both a wave and a particle.

Wave Characteristics of Light:

Light exhibits wave characteristics such as interference, diffraction, and polarisation.
Interference can result in a distinctive pattern of bright and dark spots, caused by the superposition of two or more waves.
Diffraction of light is the bending of light waves around obstacles or the spreading of light waves after they pass through a narrow opening.
Polarization of light is the phenomenon in which the oscillations of a light wave are restricted to certain directions.

Particle Characteristics of Light:

In some experiments, light behaves more like a particle, exhibiting characteristics such as the photoelectric effect and Compton scattering.
The photoelectric effect refers to the emission of electrons when light is shone onto a material. This phenomenon can only be explained by considering light as a particle.
Compton scattering describes how the wavelength of x-rays or gamma rays changes after being scattered by electrons. This phenomenon is also best explained by considering light to be made up of particles.

Key Experiments and Theories:

Albert Einstein won the Nobel Prize in Physics for his explanation of the photoelectric effect. He proposed that light is made up of particles called photons, each carrying a discrete amount of energy proportional to its frequency.
Thomas Young’s double-slit experiment provides evidence for the wave nature of light. Light passing through two nearby slits creates an interference pattern that can only be satisfactorily explained by considering light to be a wave.
Compton’s experiment showed that light can behave like a particle during scattering events, leading to the concept of wave-particle duality.

Quantum Mechanics and the Uncertainty Principle:

Werner Heisenberg’s Uncertainty Principle is integral to quantum mechanics and the wave-particle duality of light. It states that it is impossible to simultaneously accurately measure both the position and momentum of a particle.
The uncertainty principle arises from the wave nature of matter. Since waves are spread out in space, a particle described by a wave cannot have a definite position and momentum at the same time.
This principle emphasises that particles do not have intrinsically defined properties and states; instead, their properties are probabilistic.