The wave-particle duality principle is a fundamental concept in quantum mechanics which states that particles, including photons, exhibit both wave-like and particle-like behaviors. It challenges the classical theory of physics, particularly classical view of particles and waves as separate and distinct entities. The collective contributions of notable scientists such as Max Planck, Albert Einstein, Louis de Broglie, Arthur Compton, Niels Bohr, Erwin Schrödinger, and numerous others have led to the establishment of the prevailing scientific notion that particles demonstrate wave-like characteristics, and conversely, waves exhibit particle-like attributes.

When studying phenomena like interference and diffraction, light behaves like a wave. Interference occurs when two or more waves meet and either reinforce (constructive interference) or cancel out (destructive interference) each other. Diffraction refers to the bending of waves around obstacles or edges. These phenomena can be observed when light passes through narrow slits or encounters obstacles, resulting in alternate dark and bright fringe patterns.

The particle-like behavior of light is observed when studying phenomena like photoelectric effect. The photoelectric effect involves shining light on a metal surface, which leads to emission of electrons from the surface. When intensity of light is increased, kinetic energy of electrons remains unaltered, with only the number of emitted electrons increasing. However, when frequency of light is altered, according to wave nature of light, it should not result in a difference; yet, it's observed that the energy of emitted electrons increases. Einstein provided an explanation for these observations by proposing that light is composed of energy packets known as quanta. These quanta are referred to as photons, particles characterized by having no rest mass. This experiment confirms the particle nature of light.

de Broglie combined Planck's constant and linear momentum equations:

h is the Planck’s constant, E is energy of photon, λ is the wavelength of light and c is the speed of light.

p is the momentum of object, m is object's mass, and v is velocity of object.

This equation proposes that any moving object with mass will possess a wavelength known as the de Broglie wavelength. However, these wavelengths are noticeable in objects with very small masses. Due to the small value of h (6.626 x 10^-34 Js), objects of substantial mass will exhibit wavelengths approaching zero.