Light

Light is a form of energy is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Light itself is invisible but other things visible. The range of visible light in terms of wavelength is from 400nm to 800nm and in terms of frequency is from 400 THz to 800 THz. Light is emitted as tiny packets of quanta. This quanta is called photon. Light behaves as a wave as well as a particle and this property is known as wave-particle duality. Light obeys laws of reflection, refraction, defraction and interference.


The Electromagnetic Spectrum

Generally, EM radiation (the designation 'radiation' excludes static electric and magnetic and near fields) is classified by wavelength into radio, microwave, infrared, the visible region we perceive as light,ultraviolet, X-rays and gamma rays.

The behaviour of EM radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When EM radiation interacts with single atoms and molecules, its behaviour depends on the amount of energy per quantum it carries.

Refraction

Refraction

When a ray of light passes from a denser medium to a rarer medium, it undergoes refraction. Refraction is the bending of a wave with respect to the medium's optical density( not its density ). 

Laws of Refraction: 

1. The incident ray, the refracted ray, and the normal all lie in the same plane.
2. The Snell's law : the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the opposite ratio of the indices of refraction                                           

                                                           

                                
Refraction takes place because the speed of light is different in different mediums. In vacuum or air, the speed of light is 299,792,458 m/s or simply 3*10^8 m/s. But as it enters a different medium, the speed of light decreases because of absorbtion and remission of photons. The speed of light in water is 2.25*10^8.


        Refractive index: Refractive index is the ratio of speed of light in vacuum to the speed of light in the respective medium. It is denoted by μ. μ =   Speed of light in vacuum 
                                                                 Speed of light in the medium.


A list of Refractive index are given below:

Material	μ(Refractive Index)
Vacuum	1
Air at STP	1.000277
Helium	1.000036
Hydrogen	1.000132
Carbon dioxide	1.00045
Benzene	1.501
Water	1.3330
Acetone	1.36
Diamond	2.419