# Wave-particle duality

One of the fundamental concepts in quantum physics is the wave-particle duality exhibited by all matter. At quantum scales, waves are observed to behave like particles and particles like waves.

The **photoelectric effect** is an example of how a wave (electromagnetic radiation) behaves like a stream of particles (photons) when interacting with metals.

Similarly, a beam of electrons (a group of particles) exhibits **diffraction** (normally only exhibited by waves) after passing through a grating.

The French scientist Louis-Victor de Broglie (pronounced as "broy") introduced the notion that all particles have a wavelength (a characteristic of waves) and equivalently, all photons (which are components of waves) have a corresponding momentum (a characteristic of particles).

This is given by the de Broglie relation: $$$\lambda=\frac{h}{p}$$$ $$\lambda$$ is the wavelength of the particle/photon, $$h$$ is the Planck constant and $$p$$ is the momentum of the particle/photon.