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blue" "why is the sky blue class 10" "physics behind the
blue sky" "Why is the Sky Blue" "why are clouds white" "scattering
of light" "earth's atmosphere" "blue sky why"
Some of the common
questions that gets asked are why is the sky blue? While the clouds aren't? Why
is the sun yellow? And why does it look orange or reddish at the sunrise and
sunset These questions might look tough to answer at first, however, the physics
behind them is very simple. There are two things that play an important role in
giving a color to the sky.
One is the
atmosphere of the Earth and the other is the sunlight of course. So, we need to
know all about these two first.
The white light
coming from the Sun is a mixture of seven primary colors, and each colored
light has a corresponding frequency and wavelength associated with it.
The violet colored
light has the shortest wavelength of all, while the red one has the largest
wavelength and what forms the Earth's atmosphere. The Earth's atmosphere is
mainly composed of gases, dust particles, water droplets and water vapor. among
the gases, nitrogen is present in abundant quantity at around 78%.
It is followed by
oxygen which is approximately 21% and the remaining is filled with the likes of
argon, carbon dioxide and other gases. First, let's see what happens when the
sunlight falls on these air molecules.
When sunlight
strikes these molecules, it gets scattered. scattering is a process in which
the light is absorbed by the atoms and re emitted back in various directions.
However, not all
the light is scattered equally. The
amount of light that scatters is defined by the Rayleigh law of scattering. It says that the amount of scattered
light or the intensity of the scattered light is inversely proportional to the
fourth power of the wavelength of a wave.
I is inversely
proportional to lambda to the fourth power. if the value of lambda increases,
then the intensity will be lower. If its value decreases, then the intensity of
scattering will be more. lesser
is the wavelength more will be the scattering. So
now I want you to tell me, among the seven colors of sunlight, which one will
be scattered the most, yes, the light of the color corresponding to the
smallest wavelength will be scattered the most.
So blue, indigo
and violet light will be scattered most by these molecules of air. And
when this light enters our eyes, the sky appears blue to us. But wait, the
violet light has the smallest wavelength, then why doesn't the sky appear
violet or even Indigo for that matter? It is true that the sky scatters the
violet light more than the blue light. However, we don't see violet sky, do we?
What's the reason? The following graph tells us how much of a particular
wavelength is emitted by the sun. Observe the graph well. As you can see, the
sun emits more blue and light blue light compared to the violet light.
Hence more blue
light is scattered by the air molecules resulting in a blue color of the sky.
And another reason why we cannot see violet light is because our eyes are more
sensitive to blue light than to violet light. So, this is about how the gases
present in the atmosphere scatter light to dust particles and water droplets
also scattered light? Yes, they do. They scatter light as well. However, their
size is comparatively much bigger than the size of the light waves. And hence
they scatter all the colors of light in equal amounts. So, the white light which
is entering the cloud or the dust particles emerges out as white light again,
hence the clouds appear white.
There's question remains
to answer.
Why does the sun appear reddish during sunset and yellow otherwise we will see that in our next article. please share this article if you liked it. and follow my blog for more such science based articles. thank you.
