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Introduction To Light | Properties of Light | Introduction to Light | properties of light | letstute - YouTube
Channel: Let'stute
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Hello friends, in this session, we are going
to talk about something that we have seen
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throughout the course of our life.
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Something, which we see a lot and of which
we understand only little about.
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It is what separates the day from the night.
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Its what you want to see when you are in the
darkest hour and hope things are going to
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be alright.
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It comes in many colors, but collectively
its white.
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When it comes to speed, nothing can be compared
to the power of its flight.
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Believe it or not, its also responsible for
the joy of sight.
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What is it ????........Its light.
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Whether its the enjoyment of looking at our
self in the mirror or the beauty of nature
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or this colorful world we live in, at the
very base of our good fortune, is the phenomenon
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of light.
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For centuries, across many cultures, the sun
has been considered as the giver of life on
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earth and has been worshipped as a source
and symbol of light.
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So what is the relation between light and
life??
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Well that�s easy �.in our biology videos
we have seen how sunlight is responsible for
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food production in plants, maintaining the
balance of the water cycle and for general
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health But, understanding what light is and
what it does is a bit more challenging.for
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that we will have to look beyond what we see.
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Dont worry we will cover that gradually in
this session.
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Depending on where it originates from, the
sun, the moon, lightning, certain types of
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glowing insects, worms and fishes etc. are
all examples of natural sources of light.
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While, a candle flame, various types of torches,
lamps, and light fixtures are amongst the
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artificial light sources.
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Now lets understand this, our sun emits light
.really strong intense light or radiation
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called electromagnetic radiation or EMR.
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The radiation is called electromagnetic because
it contains both electric and magnetic properties.
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Electromagnetic radiation is a large family
consisting of seven members known as The Electromagnetic
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Spectrum.
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One particular family member which lies in
the middle of the spectrum, falls on the earth
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and which our eyes detect is called visible
light or the visible spectrum.
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Its so small, that if we consider the entire
EM spectrum to be around say 2,500 miles,
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the visible fraction would be just one inch!!!!
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It is within this inch that we live in our
world of natural and extra ordinarily high
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definition colour.
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We enjoy this privilege of colour due to the
presence of certain specialized cells in our
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eyes called rods and cones which we have come
across in our previous video.
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We have also seen what could happen if theres
any problem with these cells.
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Now, the other types of electromagnetic radiations
are also called light, but not visible light,.
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so automatically they are considered by us
to be invisible.
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So now we know the light which we have naturally
been introduced to since birth and that we
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see throughout our life is actually radiation..and
radiation of a good type thats an important
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source of energy for life on earth as we have
seen earlier.
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Now, just as members of a family differ from
one another and have their own unique identity,
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so also, these fractions of radiation, although
part of the same family of light, are slightly
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different from one another.
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This difference is due to three factors that
are interdependent and give each member, its
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individuality.
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These factors are Wavelength, Frequency and
Energy.
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Lets look into what these are.
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CONCEPT OF WAVELENGTH, FREQUENCY AND ENERGY
Imagine the light that we know to be represented
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in the form of waves in an ocean like this.
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What differentiates a wave from calm waters
is the presence of an area of elevation and
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an area of depression.
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In terms of our representation, the elevated
area is called a crest, while the depression
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is called a trough.
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Wavelength is nothing but the distance between
two successive crests or two successive troughs.
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The smaller the distance between the crests
or troughs, the shorter the wavelength and
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vice versa.
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Now lets consider the case of a rough sea
and a relatively calm sea.
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When we look at any part of the water for
say one minute, we notice, for that one minute
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where we look, the rough sea has more no.
of waves passing us by, which are shortly
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spaced from each other while the calmer sea
has fewer waves which are far apart.
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So, the no. of waves passing us, in the area
we observe, for the time of one minute is
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referred to as the frequency of waves.
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Thus for the rough sea the frequency of waves
is greater as compared to the calm sea.
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We just mentioned that for the rough sea the
waves are closer to one another.
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Closeness means shorter space between waves
which in turn means shorter wavelength.
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So, in all, we can conclude that the as wavelength
shortens, the frequency increases and vice
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versa.
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The third factor is also easy.
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If you have stood near the sea when its wavy,
you would have noticed the surrounding to
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be windy.
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Thus, for more no. of waves to be formed,
the wind energy or just plain energy associated,
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is greater for the rough sea than that, for
the calm sea.
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So now we will update our observation.
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Now lets join the dots as the wavelength shortens,
the frequency increases and the energy increases
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too and vice versa]
The three factors are different for each member
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of the Electromagnetic spectrum.
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Now just because we cannot see the other types
of radiations there are doesnt mean that they
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arent there or that theyre not useful.
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. Lets go back to the EM spectrum.
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To the left we have radiations of the longest
wavelength and thus the lowest frequency and
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energy.
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These radiations are called radio waves.
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They are used for broadcasting TV and radio
signals because they can cover a greater distance
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through the atmosphere due to their large
wavelength.
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As we move towards the right of the spectrum,
the wavelengths keep getting shorter and the
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frequency and energy keep on increasing.
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Next to radio waves we have micro waves used
in appliances like the microwave . They are
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also used in channels of telecommunication
like mobile networks, Bluetooth and Wireless
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LAN protocols.
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Next we move to Infrared.
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This region of the spectrum is more known
for the aspect of heat associated with it
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as they have higher energy as compared to
radio waves and microwaves.
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They are used by appliances like grills and
electric stoves for heating and cooking food.
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IR is also used as a part of heat therapy
to relieve aches and pains.
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(Fun fact: Did you know that reptiles like
the snake view their surrounding through IR
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just like how we do the same through visible
light ??)
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We have earlier seen how we the visible light
makes the world visible to us and adds colour
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to our world.
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So this part of the spectrum is associated
with the various types of light fixtures the
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ones we enjoy (like disco lights and room
lights), and the ones that are really important
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(like traffic signals and airport runway signals).
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Apart from us humans, animals like dogs, cats,
mice , monkeys etc. also see in the visible
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spectrum, though their sight is not as good
as ours.
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The part of the EM spectrum from radio waves
to visible light have comparatively lower
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energy so these radiation are referred to
as low energy radiations which are safe even
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after prolonged use.
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From ultraviolet to gamma rays, the energy
associated is now higher, so these radiations
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are referred to as high energy radiations.
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These radiations are penetrative in nature
and thus considered comparatively dangerous,
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where exposure to it, is kept to a bare minimum.
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If these radiations have to be handled over
longer periods, then appropriate precautions
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are taken.
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Moving further we have UV radiations.
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The uses of ultraviolet radiations are also
widespread in various aspects of life.
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They are used as sterilizing agents by the
medical industry and by water purifiers to
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get rid of harmful bacteria.
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It is used by dentists to harden teeth fillings
and by banks to detect fake currency notes
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by observing symbols or patterns on the notes
that are only visible under UV light.
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Another amazing fact is that certain organisms
like insects form an image of their entire
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surrounding using only UV radiations.
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X rays, as we are aware, are also used to
a great extent by the medical industry to
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examine the state of bones or foreign objects
in the body.
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It is also used by airport security to scan
luggage for potentially dangerous objects.
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Gamma rays are a type of radiation with the
lowest wavelength and the highest energy.
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They are the exact opposite of radio waves.
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They are emitted by radioactive material,
given off during nuclear explosions and during
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certain types of thunder storms.
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But despite their fearful reputation, they
are used to kill cancer cells, for medical
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and security scanning and also by space observatories
for astronomical observations.
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So far weve discussed how all these types
of radiations differ from one another.
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But as they are all part of one big family,
they have something in common too - Despite
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differences in their wavelength, frequency
and energy, they all travel with the same
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speed approximately 300 000 000 meters per
second.the fastest known speed in the universe.
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Now, as we conclude this session, lets have
a quick recap of what we learnt today.
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1) We learnt that light visible or otherwise
is a type of radiation called Electromagnetic
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radiation.
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2) Electromagnetic radiations are of seven
types collectively belonging to a large family
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called the electromagnetic spectrum.
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3) What differentiates them are factors of
wavelength, frequency and energy.
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4) What unites them is their property of speed.
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But before we go away heres a little something
interesting.
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In both these images we see the same light
behaving differently with different matter.
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Do you know what these behaviors are?
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Ok heres a hint they both begin with the letter
R. You can write you answers in the comments
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box below and tune into our subsequent videos
to know more about them in detail.
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Thats it for today.
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We hope that this session has been interesting.
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