Light might be considered the essence of life. The absence of light would make the world a dark place where we will not be able to see any object, much less interact with it. It is understandable then that light and its interaction with matter are studied extensively in physics under the branch called optics.
Light has a dual nature, it exhibits wave-like properties as well as particle-like properties. However, its wave-like nature was discovered much later and so there was a schism upon the discovery in the field of optics. In geometrical optics, light is considered as a ray or a collection of rays which interact with matter and give rise to various phenomena, whereas in physical optics the wave-like nature of light is explored.
Classical and modern approaches
The branch of optics is divided into two main study systems. The modern approach is based on the quantum mechanics and became popular only in the 20th century. The classical approach has been followed since long before and it is not obsolete as various instruments and devices have been constructed and applied which are based on the classical model of light. Under the classical model, the field is further sub-divided into geometrical optics and physical optics.
Geometrical or ray optics considers light as a ray which propagates in a straight line and is governed by the laws of reflection and refraction when interacting with matter. The construction of mirrors, lenses and their working is described by ray optics. The formation of rainbow can be explained with the help of the principles of reflection and refraction. Rainbows are formed as a result of splitting of light into its components and the process is known as dispersion. Light is also scattered when it interacts with any object. The reason for the illumination of objects in a room with minimal light is dispersion. The particles of light are bounced off objects and enter our eyes, enabling us to see the objects.
Light is a wave too
With the help of experiments and observations, physicists were able to discern the wave-particle duality of light. Physical optics is concerned with the treatment of light as a wave or, more specifically, as an electromagnetic wave. The superposition principle that is common to the nature of waves is applicable to light waves as well. According to this, when two waves interact with each other, the resulting wave is a simple combination of the disturbed effects of the component waves. The interference of light waves can be constructive, in which the resultant wave has a higher energy, or the interference can be destructive interference, leading into a lower energy wave.
Among the various optical instruments the natural instrument eye is most fascinating. The construction of the eye is studied in detail in the field of optics along with its working. A microscope is an optical instrument that allows us to see objects which are so small that they cannot be perceived by the naked eye. A telescope is another optical instrument which allows us to see objects which are farther away in space, such as planets and the moon.