Dual Nature of Light

Dual Nature of Light

Definition:

The dual nature of light can be defined as that the light can interact like a particle as well as a wave. When light interacts like a particle, it travels in straight lines.

When light interacts like a wave, it undergoes diffraction and interference.

Diffraction means bending of the waves happens around the edges of the obstacles.

From Thomas Young’s double-slit interference experiment, we can declare that light can interact like a particle. In Young's double-slit interference experiment, the light is passed through a double-slit. The light coming from two different slits either gets added together or gets canceled each other. Then, it forms the interference fringes. This phenomenon (interference) is possible only if the light interacts like a wave. When the crust or trough of the two waves interacts gets added and the crust and trough of the two waves interact cancel each other.

Louis de Broglie stated that the moving particle can have the properties of a wave whatever its nature. According to de Broglie, the wavelength of the moving particle is directly proportional to Planck's constant and inversely proportional to the momentum of the particle. The waves associated with the particles are called de Broglie waves or matter waves.

Davisson and Germer’s study of the experiment of matter waves gave evidence to the hypothesis of de Broglie that a moving particle can have a wave nature. The wavelength of the diffracted electron which was calculated based on Davisson and Germer’s experiment is in good agreement with the wavelength of the wave which was calculated using de Broglie's hypothesis.

Einstein declared that light behaves like a particle called a photon. The photoelectric effect verifies that light exhibits particle nature and also has quanta of energy which is called the photon. The photon is a massless particle having energy and momentum and travels with the speed of light. This particle-like nature of light is proved by Compton scattering of X-rays. Compton scattering of X-rays can be treated as a particle collision experiment between an X-ray photon and an electron that is loosely bound. The Compton effect was explained by the quantum theory of radiation.

• Light can interact like a particle (i.e., photon) as well as a wave.
• When a light behaves like a particle, it moves in straight lines. The particle nature of light is confirmed by the photoelectric effect and Compton scattering of  X-rays.
• When a light behaves like a wave, it undergoes diffraction and interference. The wave nature of light is confirmed by Thomas Young’s double-slit interference experiment and the study of experimentation of matter waves by Davisson and Germer.