Is Rainbow Formed Due to Diffraction?


No, a rainbow is not formed due to diffraction. Well, diffraction doesn't even play any role in the formation of a rainbow. Reflection and refraction takes part in the formation of a rainbow. If you want to know how reflection and refraction forms rainbow and not diffraction read further.

Role of diffraction in the formation of rainbow:

So as I have told earlier diffraction does not play any role in the formation of a rainbow. Well, it may look like that rainbow is formed due to diffraction because white light from the sun gets separated in seven colours by water droplets present in the atmosphere which creates a rainbow.

Why the rainbow is not an example of diffraction ?

Well, you may be wondering that rainbow colour design is an example of diffraction whereas rainbow itself is not? So let's clear out this query and if you want to know more about different examples of diffraction just like the CD one. I have a whole post on my site, in which I have explained 8 total examples and application of diffraction. Click if you wish to learn about different examples of diffraction.

So white light splits into seven colours of the rainbow by two methods. The first method is to pass light through a medium which shows dispersion because refractive index varies for a different wavelength of lights so when white light is passed through disperse medium different colours of light in a dispersing medium will have different refractive index depending upon their wavelength. 

prism split white light
prism split white light


P.s: Prism uses the same method to spilt white light into 7 different colours of the rainbow. 

The second method is to use diffraction grating where white light is passed through many closely packed slits which split the light into seven colour.

Well, a rainbow is formed because of water droplets present in the atmosphere. It may look like diffraction is taking place in water droplet which forms but in reality there are no slits present in water droplets which can split white light into seven colours.

It's actually more like the first method which we have discussed where dispersion medium of light is changed from air to medium inside water droplets due to which white light get splits into seven colour.

So diffraction doesn't play any role in the formation of rainbow. Well it may look like a rainbow is formed due to diffraction but in reality, it is formed due to change in a dispersion medium of light from air to water droplet. Refractive index is changed which splits white light into seven colours.


How is a rainbow formed ?

So we all know until now that rainbow is formed due to a splitting of white light by water droplets present in the atmosphere after rain but there are some other things which go along as well such as refraction and reflection.

Formation of a rainbow by water droplets
Formation of a rainbow by water droplets

Role of refraction and reflection in rainbow formation:

Now it's clear that diffraction doesn't play any role in the formation of a rainbow. In rainbow formation, we all know that white light splits into seven colours when light enters in water droplets and there is a change in a dispersion medium.

Due to change in a dispersion medium, the refractive index of a medium is different for different wavelength and light gets diffracted according to wavelength and this is how seven colours of rainbow splits from white light because every colour of light has their own unique wavelength.

In this whole process of splitting of light refraction and reflection, both phenomena takes place. First, let's learn about refraction and reflection.

So before learning where reflection and refraction take place in the rainbow formation, it's mandatory to know the proper definition of both of them. In optics, many people get confused including me regarding some terms because they all seem so similar but with a small difference. So let's understand what is refraction and reflection.

What is a reflection ? 

When light travels in one medium trying to enter another medium and encounters an obstacle in the second medium. Light gets bounced back after encountering of obstacle and stays in the first medium only.

Representation of Reflection, Refraction and Diffraction
Representation of Reflection, Refraction and Diffraction
This phenomenon of bouncing back of light after encountering of obstacle in its path is known as reflection.

Light gets reflected back in two ways:

1. Specular:- Light gets reflected back in a single direction as described by law of reflection. 
2. Diffuse:- Lights get reflected back in many different directions.

What is refraction ?

Well, unlike reflection, refraction doesn't encounter any obstacle and therefore it can easily be able to enter into the second medium instead of bouncing back but due to change in medium, light wave shows certain property and light gets dispersed. This dispersion is based upon the light. Different colours of light with different wavelength will have different dispersion.

Refraction
Refraction

P.s: Different colours of light dispersed differently because refraction depends upon wavelength.


Refraction is a phenomenon in which light waves travel from the first medium to the second medium and get dispersed. Dispersion is different for different wavelength of light. 

P.s;- Medium refers to space in which light wave travels.


Where reflection and refraction take place in rainbow formation ?

So now you know the basics of reflection and refraction. So where does reflection and refraction take place in rainbow formation?

We know that white light from the sun splits due to water droplets present in the earth's atmosphere and due to this rainbow formation takes place. 

A rainbow appears bright due to reflection takes place inside water droplets and it splits into seven colour because dispersion is different for different wavelength of light. 

Let's understand how this happens:)

Water droplets are able to split white light into seven colours because when light enters inside water droplets, refraction takes place and light get dispersed into seven colours because different colour and wavelength of light will get dispersed differently. 

Then light waves get reflected inside water droplets due to which it appears shinner. After that light waves leave the water droplet and refraction takes place again and this is how sunlight splits into seven colours and the rainbow appears brighter.

Conclusion:

Diffraction doesn't play any role in the formation of a rainbow. Well it may look like diffraction is taking place in rainbow formation but a rainbow is formed due to a splitting of white light from the sun into seven colours by water droplets present in the atmosphere of the earth.

Water droplets are able to split white light with the help of the phenomena of refraction and reflection. Due to refraction white light which consists of seven colours each colour gets dispersed differently in refraction due to different wavelength if each colour and rainbow appears brighter due to reflection which takes place inside water droplets. 

So rainbow is not formed due to diffraction but by reflection and refraction taking place inside water droplet present in the earth's atmosphere.

F.A.Q:

Q.1 What is the first and second medium in refraction and reflection of light ?

Medium refers to anything where the light wave can travel. For example air, water, etc. 

Q.2 What is the example of real-life refraction ? 

In our bathroom or kitchen, we can take the first medium as air and second medium as water then light enters from air into water and refraction takes place.

Q.3 Why white light from the sun splits into seven colours when a light wave enters into water droplet ?

White light consists of seven colour. Each colour has a different wavelength and when white light enters water droplet medium gets changed and refraction takes place. In refraction, light gets dispersed depending upon the wavelength thus each colour of light has different wavelength all seven colour gets dispersed according to this and this is how white light splits into seven colours of the rainbow.

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