Question

why does a stick partly, immeresed in water, appear to be bent? explain with a diagram.

Answer 1

The stick appears to be bent....
True!!

Principle = Refraction of Light.

Working :-

When we immerse a pencil inside the water the part of pencil inside the water appears to be bent.

This happens because of the refraction of the light which creates an illusion that pencil is bent.

REFRACTION OF LIGHT :-

The diversion of light from its original during a travel from one medium to another is referred as Refraction of light.

Rules Of Refraction :-

1) When a light ray travels from an optical denser medium to optical rarer medium, The ray gets deflected away from normal.

2) When a light ray travels from optical rarer medium to optical denser medium, it gets deflected towards the normal.


Coming back to the question! :-

When air and water are compared, we get to know that air is optical rarer while water is optical denser medium.

So, Following the rules of Refraction, Light bends its path.
But where?? !!

Since, The light is traveling from an optically denser medium to optically rarer medium, it will follow the first law of Refraction and will bend away the normal....

Bending of the light away from the normal creates the illusion.
But how..?

Carefully look at the attached picture.

You will notice that the rays are coming in straight path from the pencil.
But as they reach the surface of water they refract and turns away from the normal and reaches our eyes.

But, Here's the twist!!

The eye predicts that the rays are coming from a straight line (refer the dotted lines in image)
And it assumes that the pencil is at a position which is above the water surface.

This is how pencil appears to be bent.

If you look carefully, you will find that it was an illusion and our eyes got fooled.
Similarly,
If you drop a coin in water it will appear to be very close to the surface.
Also, very deep swimming pools appear to be shallower than their actual depth.

This is all because of the Refraction of the light.

ABOUT THE IMAGE (ATTACHMENT) :-

(i) is the optically denser medium.
(ii) is the optically rarer medium.

Red coloured lines are the lines by which light rays travel.
Dotted lines are the rays which our eyes predict.
Yellow lines is the actual pencil ;and
Green lines are the ones which show the position which our eyes see.


Thanks!