Question

Which theory explains all the characteristics of light?

Answer 1

Light has dual character. It acts both as a particle and wave.
In some experiments like diffraction, interference, light acts as a wave. In experiments like the photoelectric effect, light exhibits particle-like properties.
Einstein gave a relation between wave and particle nature of light.

Complete step by step answer:
Quantum theory of light explains the characteristics of light. Quantum theory states that both light and matter consists of tiny particles which have wavelike properties. According to Einstein’s theory, light is composed of particles called photons, similar to matter which consists of electrons, protons and neutrons.
Light acts as a wave in some experiments like diffraction and interference; and as a particle in others like photoelectric effect. But, light do not exhibit both kinds of properties simultaneously i.e. Light either behaves as a particle or as a wave at any instant.
Einstein gave a relation which related particles and wave nature of light. According to Einstein, light is made of particles known as photons. Each photon have energy $E=h\nu$ where h is Planck’s constant and it is equal to $h=6.63\times {{10}^{-34}}\,Js$, $\nu$ is the frequency of wave associated with it.

Additional Information: Wave is defined as the disturbance that travels through a medium, without transporting matter, transporting energy from one location to another.
A particle is a small localised object. A particle can be described by several properties like volume, density or mass.

Note: Every moving particle has a wave associated with it which is known as matter wave.
Light exhibits both particle and wave like behaviour. It acts as a particle in some experiments and shows its wave-like behaviour in others.
Light is an electromagnetic wave and can travel through vacuum also.