Introduction to refraction of light

 

INTRODUCTION TO REFRACTION

REFRACTION: Refraction is one of the phenomena of light, where light gets deviated from its original path when it enters from one medium to another medium. This happens because of change in the speed of light.

OPTICAL MEDIUM:

An optical medium is material through which electromagnetic waves propagate (example light)

In terms of optics media is classified as whether denser or rarer depending on its optical density. Optical density may not be comparable to mass density of a medium.

For example we know kerosene floats on water because mass density of kerosene is less when compared to water. But in terms of optics kerosene is denser medium than water.

So how to decide whether a medium is optically denser or rarer?

It depends on its ability of allowing light through it.

As kerosene cannot allow light as free as water, so it is denser medium when compared to water (in terms of optics).

So if you compare any two media, we can find one is denser and one is rarer or sometimes both may have same optical densities.

It’s very important to note that when light enters form rarer medium to denser medium it loses its speed. Similarly when light enters from denser medium to rarer medium it gains speed. That is why bending of light takes place as a result it gets deviated from its original path.

“The process of changing speed at an interface, when light travels from one medium to another resulting in a change in direction” is refraction of light. The process of refraction involves bending of light ray

 

Understanding bending of light:

How can we conclude in which direction light gets deviated when it pass over two different media?

Let us understand with an example:

Let us assume R be rarer medium and D be denser medium.

The line which is separating two media is called interface.

The line drawn perpendicular to interface is called normal.

The point at which incident ray falls on interface is called point of incidence.

Now let us assume that light is entering from rarer to denser medium.

 

let angle of incidence be “i” and angle of refraction be “r”

As shown in the above figure light bends towards normal as it loses its speed when it enters from rarer to denser medium. In this case (i>r)

Similarly light bends away from normal when it enters from denser to rarer medium as its speed increases. In this case (i<r)

Observe the figure below

IMPORTANT: we have two conditions where refraction will not takes place.

1)    Refraction will not take place when incident ray is sent along the normal to the interface. Here i=0 and r=0.

2)    Refraction will not take place when refractive indices of two media are same.