Rainbow

What is a Rainbow?

Rainbow is one of the well-known optical effects that are related to weather, and one of nature's most glorious masterpieces which result from the refraction of sunlight from falling water droplets plus the reflection of the light from the back of the droplet.

It's an excellent demonstration of the dispersion of light and proof that visible light is composed of a spectrum of wavelengths, each associated with a distinguishing color.

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You will be surprised to know that you can even see it on sunny days when you are near the waterfalls or fountains.

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             Rainbow in waterfalls                                               Rainbow in fountains

What Are the Rainbow Colors?

We know that rainbows are made by the dispersion of white light by the water droplets.

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Rainbow has seven primary colors in the order of ROYGBIV, i.e., red, orange, yellow, green, blue, indigo, and violet.

What Makes a Rainbow?

We can see anything because the light falling on our eyes, enables us to view them.

Similarly, the red light coming from the upper part of the rainbow reaches our eyes enabling us to see it.

When we look at this color, we would wonder where this light is coming from?

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Let’s consider a single droplet in the red color region, a ray of white light incidents on the surface of it, will reflect some light in the boundary and refract some of it.

The reflected light is white again, and it goes away from our eyes, so we ignore this as this light doesn’t help in forming rainbows.

We know that the white light of the sun is composed of seven colors which are VIBGYOR.

When this white light is passed through the prism, it breaks this white light into its constituent seven colors.

The water droplets during rainfall behave exactly like a prism.

They disperse the white sunlight at the entry point, then this dispersed light falls onto the rare side of the droplet and each light color is again refracted by different angles.

If you observe, this light gets refracted in the same medium.

Here, you can see the light didn't pass from the water droplet to the air.

Well, this happens because of an optical phenomenon known as the total internal reflection.

Generally, when the light passes from denser to rarer medium, it bends away from the normal.

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However, in the case of total internal reflection, there is an angle called critical angle, ic, the angle at which the refracted ray becomes perpendicular to the normal.

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If you further increase the angle of incidence, the refracted ray remains in an incident medium.

Here, you can notice that a ray of light gets reflected in the same medium.

The same thing happens with the water droplet as well, this angle of incidence at this surface for each colored light is such that they all bend in the same medium, so these different colored light rays are now at the air-water interface again for the third time. However, at this time, the total internal reflection doesn’t occur and these rays bend in the air but now these rays are separated by some amount.

This is because the three refractions created a larger gap between these colors, so all the water droplets in the red region of the rainbow behave in the same manner.

You can see the red color only while all other light colors got refracted.

This is because only the red color from this region reaches our eyes while all other colors are refracted at such a large angle that they don’t reach our eyes on the ground. Similarly, it happens for the region of other colors as well.

This is how rainbows form in the sky.

How to Make a Rainbow?

Things required to make rainbows are:

1. Granulated sugar

2. Coloring tablets or food coloring water

3. Straw

4. Six glasses

5. Measuring spoon

Instructions

Fill each glass with water and add different amounts of sugar in each glass numbered from 1 to 5.

1. Add 0 tablespoon of sugar and red color to it.

2.  Add one tablespoon of sugar and orange food color to it.

3.  Add two tablespoons of sugar and yellow food color to it.

4.  Add three tablespoons of sugar and green food color to it.

5. Add four tablespoons of sugar and blue food color to it.

6. Add five tablespoons of sugar and food color to it.

Stir these glasses until the sugar is dissolved.

Now, transfer about half of the blue into the empty glass, slowly add green water of the same amount on the top of the blue water, and do the same for the next colors.

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You can see a beautiful rainbow. 

How to Create a Rainbow?

Materials Required

1. Water 

2. Sunlight

Tools

1. Prism

2. Whiteboard

Method 

1. Place a whiteboard on the ground under the sunlight.

2. Place the prism above the whiteboard.

3. Now, rotate the prism at certain angles until you get a rainbow.

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