Refraction of light

 

Refraction of light

Refraction of light:--

                                  Refraction of light is the bending of light, When ray of light travel through one medium to another medium. The speed of light is maximum in the vacuum.

During refraction , the frequency of light remains same but the speed of light and wavelength changes.

Refraction of light observed in many places in our daily life. When any object is  immersed in the water. These object appears closer than the real position.

Some natural phenomena including rainbows and mirages is also observed due to refraction of light.   

Some examples can be taken:--

When a coin is poured inside the filled water bucket, then the coin is appeared slightly raised above its actual position due to refraction of light.

 

Refraction through a rectangular glass slab:--

 

To understand the phenomenon of the refraction of light through a glass slab, we should take a paper sheet and place a glass slab over the white paper sheet. And draw the outer line of the glass slab. And name it as ABCD.

Take four identical pins and fix two pins (E and F) vertically such that the line joining the pins is inclined to the edge AB.

And then look of the image of the pins E and F through the opposite side of the slab.

And then fix the pins G and H in such a manner that these pins E and F and their images  all  lies in the straight line. And then remove the pins and the slab.

And then join the all position of the tip of the pins E and F and  create a line up to AB edge. Let EF meet AB at O.

And then join the all position of the tip of the G and H  and create a line up to CD edge. Let GH meet CD at  O’.

Join the O and O’

By joining this line we get that the ray of light are changed its direction at point O and O’.

It is noted that the both point O and O’ lie on the surface are separating the two transparent medium.

The ray of light at point O enters from a rarer medium to denser medium. It means the ray of light is entered through air medium to glass medium.  And we observed that in this case the ray of light is bent towards the normal.

Similarly, the ray of ligh at point O’ enters from a denser medium to rarer medium. It means to say that ray of light is entered through the glass medium to air medium. And we can observed that in this case the ray of light is bent away from the normal.

And we compare the angle  of incidence  with the angle  of refraction for  both refracting surface of the glass medium AB and CD.

Here , a ray of light EO is incident on the surface AB is called as incident ray.

OO’ is the refracted ray

The O’H is the emergent ray.

Here it is noted that the incident ray of light is parallel to the emergent ray of light.

Refraction is due to the change in the speed of the light, when the light of rays enters from one transparent medium to another transparent medium.

 

 

why   incident ray of light is parallel to the emergent ray of light ?

The ray of light  enters from a rarer medium to denser medium. It means the ray of light is entered through air medium to glass medium or (air – glass interface ) .  And we observed that in this case the ray of light is bent towards the normal.

Similarly, the ray of light enters from a denser medium to rarer medium. It means to say that ray of light is entered through the glass medium to air medium or (glass- air interface). And we can observed that in this case the ray of light is bent away from the normal.

These extent of bending of the ray of light at the opposite parallel faces air- glass interface and glass- air interface of the rectangular glass slab is equal and opposite. That is why the emerges ray parallel to the incident ray.

 

 

Law of refraction of light :--

 

The incident ray, the reflected ray and the normal to the interface of the two transparent medium at the point of the incidence , all are lie in the same plane.

The ration of the sine of angle of the incidence to the sine of the angle of the refraction is a constant, for the light of a given colour and for the given pair of the media. This law is also called as snell’s law of the refraction. This is true for the angle 0<i<90

 

If the angle of the incidence is – i

The angle of refraction is ---- r

Then ,

 

 

                         Sin i

Constant = ……………….

                          Sin r

 

Here the constant value is also called as refractive index of the second medium with respect to the first medium.