Question : How light can be treated as a wave ?
In 1679, Huygens proposed the wave theory of light in which he said that each point of a source of light sends out waves in all directions. The locus of all particles vibrating in the same phase is called wavefront. Each point of the wavefront acts as a centre of new disturbance and emits its own set of wavelets. The locus of these wavelets in the forward direction gives the position of the new wavefront at subsequent times