Question

Explain the following i)Refraction ii) Wave mode iii)Bloch body

Answer 1

i) When a beam of light is incident on a surface separating two transparent media, a part of light gets reflected back into the first medium while rest enters the other.

The phenomenon of change of direction of light (bending of light) at interface of two media, when it goes from one media to another is known as refraction of light.

CAUSE OF REFREACTION:

The refraction happens due to different velocity of light in different media. Consider a slab and explain.

Now explain the bending towards or away. Memorize using an apple a day keeps doctor away. Also explain normal incidence.

When light goes from one medium to another, the frequency and phase of light do not change but velocity and wavelength of light changes

ii) The microscopic phenomenon like interference and diffraction could not be accounted by ray optics. To explain these phenomenon, wave concept of light i.e wave optics was introduced.  

Light : a wave or particle

            Newton believed that light is a collection of particles (corpuscles of light) and these particles travel in straight lines when not acted by external forces.

           But Huygens (1629-1695) suggested that light may be a wave phenomenon. The straight motion of light may be due to the fact that wavelength of light may be much smaller than the dimensions of obstacles and openings. But at that time newton was renowned scientist so people believed in newton theory of particle nature of light.

           Young double slit experiment (1801) by Thomas Young and diffraction experiment (1850) by Fresnel challenged Newton and then it was believed that light is wave.    

           Then again drama started when photoelectric effect (1880) by Hertz could not be explained by wave theory of light. In 1905, photoelectric effect was explained by particle model of light by Einstein.

           All scientist accepted dual nature of light. Later it was found that even particles like electrons also have dual        nature.

As a wave, Light is an electromagnetic radiations having the wavelength of about to The speed of light in vacuum is the highest speed attainable in nature. Light is nonmechanical wave and it need no medium to travel. Hence it can also travel in vacuum.

(iii) A black body absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.

A black body in thermal equilibrium emits electromagnetic radiation called black-body radiation.

properties 1. it is ideal absorber 2.It is an ideal emitter