Light - Introduction

Light:

LIGHT IS A FORM OF ENERGY WHICH CAUSES IN US THE SENSATION OF SIGHT  AND  ENABLES US TO SEE OBJECTS .

CHARACTERISTICS  OF LIGHT : 

·  Light travels in straight lines.

· The speed of light are different in different medium. Speed of light in vaccume is 3 x 10⁸  m/s.

·  Light is electromagnetic wave.

· Light show different phenomenon like reflection, refraction, diffusion or scattering, polarization, interference , dispersion etc.

·  Light is transversal in nature.

Nature of Light

There are two theories about the nature of light:   

wave theory of light and particle theory of light. 

Light exhibits the properties of both waves and particles. The modern theory of light called 'Quantum Theory of Light' combines both the wave and particle models of light. 

Some of the phenomena of light can be explained only if light is considered as wave whereas others can be explained only if light is considered as particles. Thus, there is evidence for the wave nature of light as well as for particle nature of light.

According to wave theory : 

§ Light consists of electromagnetic waves which do not require a material medium for their propagation. 

§ The   wavelength   of  visible    light  waves   is very  small (being only about  4 x 10^-7 m  to  8 x 10^-7 m). 

§ The speed of light waves is very high of  3 x 10⁸   m/s   in vacuum. 

§ The phenomena of diffraction (bending of light around the corners of tiny objects), interference and polarization of light can only be explained if light is considered to be of wave nature. The particle theory of light cannot explain these phenomena. 

According to particle theory : 

§ Light is made  of particles which travel in a straight line at very high speed. 

§ The elementary particle of  light is the 'photon'. 

§ The phenomena of reflection and refraction of light, and casting of shadows of objects by light, can be explained only if light is considered to be of particle nature.

§ Wave theory of light cannot explain these phenomena.