Corpuscles Of Light:

The hypothesis of EM-wave propagation is an associatively recent addition to the storehouse of physics knowledge. Sir Isaac Newton, the seventeenth-century English physicist and mathematician known for his hypothesis of gravitation and his role in the discovery of calculus, supposed that visible light consists of sub-microscopic particles. To the casual spectator, visible light travels in straight lines via air or free space. The shadows are cast in such a manner as to recommend that there are no exceptions to this rule, at least in a vacuum. Nowadays scientists know that light behaves, in some manners, such as a barrage of bullets. The particles of EM energy, termed as photons, have momentum, and they apply measurable pressure on objects they strike. The energy in a beam of light can be wrecked down into packets of an assured minimum size though no smaller.

Though, one require not search hard to find complications with Newton's corpuscular hypothesis of the nature of light. At a boundary among air and water, photons do mysterious things. Ask any children who has ever stuck a fishing pole into a lake or who has looked into the deep end of a swimming pool and observed 4 m of water appear like 1 m. Photons change direction hastily whenever they pass at a sharp angle from water to air or vice versa (the figure is as shown below), though there is no obvious force to give them a sideways push. Whenever light passes via a glass prism, things get stranger yet; not only are light beams bent by the glass, though the extent to which they are bent based on the color!

Figure: When light rays consist of particles, what push them to one side at the water surface?