Dispersion of Light by Prism

Sir Isaac Newton, is famously known for the discovery of Gravity and the Laws of Motion.

Apart from them, there are many more studies conducted by him which expanded our knowledge about nature and Physics.

In this story, let's focus on one such experiment conducted by him using a glass prism.

Newton, observed that when white light is passed through a glass prism, it split up into seven colors.

The sequence of colours that appear on the band are $V i o l e t, I n d i g o, B l u e, G r e e n, Y e l l o w, O r a n g e, Y e l l o w$

We can remember the sequence of colors using the acronym $V I B G Y O R$ .

This band of color components of light is called the $S p e c t r u m o f L i g h t$ .

This phenomenon of splitting of white light into its component of colours is called $D i s p e r s i o n$ .

But why do light, disperses into its component of seven colours ?

If we recall, in $r e f r a c t i o n$ of light, light bends when it enters or exits from one medium to another.

Now, different colours of light refracts and bends through different angles.

The $r e d$ light bends - $l e a s t$ while the $v i o l e t$ - the $m o s t$ .

Because of this uneven bending of the different colors of light, each color emerge along different paths.

This is why white light disperses and we see a band of distinct colours.

Quick Fact : Issac Newton was the first one to use a prism and obtain the spectrum of sun light.

After obtaining this spectrum, Sir Issac Newton further tried to split it by using a prism of a different material.

But to his surprise, he could not get any more colours!

When he placed a second identical prism in an inverted position as shown, in front of the first prism...

..it allowed all the colours of the spectrum to pass through it ..

.. and all of them $r e c o m b i n e d$ after passing through the second prism and emerged out as white light!

These observations gave Newton the idea that : "Sun-Light is made up of seven colours."

Where-else can we observe the phenomenon of dispersion of light ??

Well, the best example is the $R A I N B O W$ . It is caused by the dispersion of sunlight by water droplets in the atmosphere.

Here, the water droplets act like small prisms. Sunlight, entering into water droplets, refracts and disperses into component colors.

This dispersed colors of light undergoes $t o t a l i n t e r n a l r e f l e c t i o n$ inside the water droplet, and while coming out forms the band of $s p e c t r u m$ as shown in the image.

So, because of $D i s p e r s i o$ n and $T o t a l I n t e r n a l R e f l e c t i o n$ , we are able to see the different colours of sunlight in form of a - " R A I N B O W " !

Amazing Isn't it!! We can also see a rainbow on a sunny day, when we look at the sky through a waterfall or a fountain, by keeping the Sun behind us.

Let's take a small REVISION

Dispersion of lights is the splitting up of white light into it's constituent seven colours.

Dispersion occurs because, different colors of light deviate differently, with Red light deviating least and Violet light deviating most.

When two prisms are placed in the positions as shown, the spectrum of light recombines into white light.

Rainbows are caused because of dispersion and total internal reflection of sun light inside water droplets.

Keep Exploring : )