Nature, in its true self, is a magnificent creation of God. The bounties of nature have always surprised humans. Logics behind such marvels have always been a challenge scientist likes exploring.
One such challenge was the rainbow.
Rainbows – the magical colours that come out of nowhere, have always been subject to stories and myths and continue to fascinate kids and adults alike.
However, the scientific explanation behind rainbows was understood way into the past by a German monk.
As beautiful as they appear, the science behind rainbows is simply as intriguing!
Before you read further, I want you to do a small experiment.
Take a glass of water and keep it out in the light. Stand in front of the sun and let the light flow from behind you and see what happens.
Do you see how the white light splits into seven colours? Do you notice how you made a mini rainbow of your own?
How cool is that!
But you see, rainbows take place on a much grander scale. They are spotted anywhere around the world and not just by a single person, but by an entire population.
So how is that happening?
Where are those rainbows coming from?
Why do rainbows always appear after a rain shower?
Where are these rainbows getting their colours from?
Is there actually a treasure chest at the end of the rainbow?
What is refraction?
Let’s start by discussing how light travels.
Light travels in a straight line until it hits something else. However, when light travels from one transparent medium and hits another transparent medium, the existing ray of light bends at a different angle from the second transparent medium. This bending of light from one medium to another medium is called refraction.
Refraction definition – Bending of light from one medium to another medium is called refraction.
Refraction of light is also dependent on the density of the mediums refracting the light rays. The dense medium is called a denser medium, and the less dense medium is called a rarer medium.
The refraction of light can be spotted on an everyday basis in a lot of real-life scenarios.
Notice how a straw seems deflected when placed in a glass of water.
Notice how anything below a glass table seems raised.
It’s all because of refraction!
Let’s further understand how refraction works.
Consider a glass slab.
Refraction of Light diagram
So we already know that the angle of refraction would take place twice based on what we just learnt.
First, when the light enters through the air (First transparent rarer medium) into the glass slab (Second transparent denser medium).
Second, when the light exits the glass slab (Second transparent denser medium) into the air (Third transparent rarer medium)
Law of refraction
Therefore, based on this simple experiment, we can understand the laws of refraction as mentioned below –
The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, lie in the same plane.
The ratio of the sine of the angle of incidence (Sine i) to the sine of the angle of refraction is a constant (Sine r), for the light of a given colour and the given pair of media. This law is also known as Snell’s law of refraction. (This is true for angle 0 < i < 90o)
If i is the angle of incidence and r is the angle of refraction, then,
Sine i / Sine r = Constant
Another interesting observation in this experiment is that the ray of light travels from a denser medium to a rarer medium bending away from the normal. The ray of light ray bends towards the normal when it travels from a rarer to a denser medium.
Everyday examples of Refraction
A useful aspect of refraction for people who need to wear spectacles due to refractive errors. Refractive errors occur when a person’s vision is problematic due to the light not getting focused on the retina due to the shape of the eye.
Refractive errors happen to be the most common type of vision problem.
A virtual Hi-5 to all our fellow speckies coming right up!
Another key application of refraction can be seen in the methodology of a prism. The colours that are seen through the prism occur due to the inflow of white light into the prism.
The wavy patterns of fish in an aquarium happens as light travels from one side of the aquarium and reaches our eyes through the surface of glass and water.
Video: How Rainbows are formed – Class 10th Science Refraction of Light
FAQs about refraction
1. What is a refractive index?
Refractive index is defined as the measure of the bending of a ray of light when passing from one medium into another.
2. How is the refractive index calculated?
Refractive index (n) is equal to the velocity of light (c) of a given wavelength in empty space divided by its velocity (v) in a substance, or n = c/v.
3. What is atmospheric refraction?
The refraction caused by the Earth’s atmosphere is called atmospheric refraction. The illusion of the rainbow is an example of atmospheric refraction.
Coming back to the mystic illusion of the rainbow, guess how rainbows appear by keeping in mind all that you’ve learnt so far!
Watch this short video to confirm your understanding.
Interesting, isn’t it? How marvellous it is to understand all that nature has to offer.
So folks, now that we’ve deep-dived into this concept, we urge you to trace more such examples in your everyday lives.
Because remember, when life gives you lemons, experiment!
And as for rainbows, the next time you happen to see one, feel free to flaunt your knowledge! 😉
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