Question

Which phenomenon can only be explained by assuming that light is quantized

Answer 1

Answer: The Photoelectric Effect

Light can be considered as a wave or as particles, in this context Einstein proposed that light behaves like a stream of particles called photons with an energy, in order to correctly explain the photoelectric effect.

This fenomenom consists in the emission of electrons (electric current) that occurs when light falls on a metal surface under certain conditions.

So, if we consider light as a stream of photons and each of them has energy, this energy is able to pull an electron out of the crystalline lattice of the metal and communicate, in addition, a kinetic energy.

This means the photoelectric effect can only be explained based on the corpuscular model of light, that is, light is quantized.