Light wave or Particle: Newton - Wave Optics Video Lecture - Class 12

hello friends this video on wave optics
part 2 is brought to you by example your
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make sure that you have watched part one
before going ahead with part two
question is what is left so again we are
back to square one
in our previous lesson in fact the even
the previous one that has
electromagnetic waves and your ray
optics
please take it so much about light so
now we are again asking ourselves what
is light is light a particle or a wave
so when I ask you what is light you most
of you say light is a form of energy
perfectly fine no issues but when I ask
you what is it made up of is light made
up of small small particles or it is a
wheel and a by now you all are aware
what is a wave because we have discussed
so many things about waves in our lesson
on electromagnetic waves right so what
it is this is a particle or instant a
wheel this question became a huge topic
of discussion somewhere in the 1800s and
1900s I mean the scientists some of the
scientists had this view that light is a
particle whereas some of the scientists
had a view that no light is not a
particle instead it is a wave but what
actually light is so let us quickly look
at the history I mean which which
gradually lead us to a conclusion and we
will look at the conclusion as well so
let us start with the history first the
classical time when you when Newton was
the most prominent was considered to be
the most prominent scientist as well as
the most renowned one so Newton gave one
theory he said that light is particle
nature that means light consists of huge
number of
so Newton stated this he stamped his
statements with some of the evidences or
with some of the proofs which he could
give now Antoine know that Newton was
somebody who who was a master or who had
mastery in classical mechanics right
we all have studied classical mechanics
in our in our class xi so in classical
mechanics we study all about motion like
Newton's Newton's first law and into
second law Newton's third law they all
talk about speed velocity distance
displacement acceleration so we always
talk about motion of particles right and
Newton had mastery in that field so
Newton said that light is of particle
nature and he proved it on those lines
how did he prove it he told that as I
said light is made up of small particles
and he called those small particles as
corpuscles so many times it was also
known as called the skillet theory this
theory was also known as called
postulate theory so what evidences did
he prove he told that we know some of
the phenomenon related to light right
for example the reflection of light
brief refraction of light right again
some of the facts like light travels
along a straight path so he proved all
these things using some scenarios
related to mechanics for example how did
he prove the phenomenon of reflection he
proved it stating that so if you
consider the phenomenon in mechanic's
for example when you throw a ball it
hits the wall and bounces back right now
think of a scenario of elastic collision
for example if you if you consider your
carom board when you play a carrot you
have the striker when you hit the
striker it goes back strikes the
boundary and comes back right so in that
scenario what happens when the
right goes towards the book towards the
wall of the can board that forms your
incidentally somewhat like this and then
it bounces back so this was you are
incidentally so this was your
incidentally and this was reflected ray
such that in case of an elastic
collision this angle will always be
equal to this angle so Newton explained
in this way that the phenomenon of
reflection can be explained using the
particle nature of light because light
is made up of mainly such particle I
mean here I have taken the example of a
wall or a striker in inside light there
are a huge number of small corpuscles so
each of these corpuscles they come in a
bunch they hit the wall and the goes
back so that is how the reflec
reflection of light was explained he was
also hoping to some extent able to
explain the phenomenon of refraction
however this this explanation had flaws
but somehow Newton was able to convince
people with his explanation what is the
same how did he explain about refraction
he told that light is made up of
particles as we all know now what
happens as the particle moves from one
medium to another medium this is medium
one and this is medium two this is the
real median and this is a denser medium
now what was refraction diffraction
tells that when a ray of light falls on
the boundary which separates our error
medium from a denser medium then when it
enters the denser medium it comes
towards the normal right so this is my
incidentally as again this is the denser
medium it bends towards the normal right
this is what does the phenomenon of
refraction so Newton told that what
happens is that when these small small
Cod Pasillas when they reach will they
reach towards the boundary what happens
the particles of these denser medium
they came to attack this corpuscle so
these
corpuscles get attracted by the
particles which are present inside this
medium now when the particle entered
completely inside this medium that means
when the particle is deep inside this
medium it is attracted by the particles
of the medium from all sides for example
it is suppose there is one particle
which is exactly at the boundary that
day what happens it experiences force in
this direction by the particles present
inside the denser medium but when this
corpuscle enters deep inside the medium
it experiences the attractive force on
all sides therefore the net force on
this particle becomes zero so that means
when the core person enters completely
inside the denser medium the net force
on this is zero and according to Newtons
for Newton's first law will even know
that if there is no net force on a
particle a particle will continue to
move in a straight line because we know
the law a particle at rest will remain
at rest and a particle in motion will
remain in motion as long as no external
forces applied on the particle so if you
look at this particle which is
completely inside there is no force
acting on it so this particle will
continue to move along its own path so
that is why once this particle enters I
mean once the corpuscles enter the
denser medium again they keep moving
without getting disturbed right because
the net force on them is zero so why
does this bending take this because so
Newton explained it in this way that
since because of this attractive forces
in one direction
what happens the corpuscles get
accelerated right because whenever there
is an attraction for example there is
suppose you were standing you are
suppose you are walking so you are
walking at your own speed there is no
acceleration asset now somebody your
friend comes from comes suddenly and he
drags you he attracts you so what will
happen you will start running faster
right so that means whenever there is
some attraction there is some axial
related with the particle so here also
the corpuscles get accelerated now what
happens when it gets accelerated
accelerated means nothing but increase
in velocity so now what will be the
increase in velocity the increase in
velocity takes place along this
direction like now because of this
increase in velocity what happens the
particle slightly bends towards the
normal because there is suppose if I
draw it here to explain it in a better
way for example this is the boundary
this is my rear a medium and this is my
denser medium distance that normal let
us suppose this is my incidentally right
this is my incident today with angle of
incidence I now the particles which are
present here they will have two
components of velocity one is VX and the
other one will be V 1 V Y sorry so what
happens when this particle gets
attracted towards this direction then V
Y increases due to attraction right so
this vertical component of velocity will
increase so the vertical component of
velocity will become more compared to
the horizontal component of velocity so
that means this vertical component will
increase somewhat like this therefore
the movement of the particle will be
somewhat like this because the
horizontal component becomes lesser then
compared to the vertical component and
therefore this ray of light gets bent
right so you understood how see this is
not the real fact what I am explaining
now is how Newton explained this
particle trail how Newton convinced
people that light is made up of huge
number of small particles and those
particles are called quadriceps so he
explained that using this corpuscles
sharing we can explain the phenomenon of
reflection that a it is like the
corpuscles fall on the boundary and they
bounce back
similarly explain the refraction stating
that these small part
of light when they reach towards the
medium they get attracted by attracted
by the molecules or by the particles of
the denser medium as a result of which
the corpuscles get accelerated and they
went towards the normal
Newton also explained the rectilinear
motion of light how did he explain that
he told that let us suppose there are
two rules side by side which are
separated by one what happens if the
window of this the first room is open
light enters the room but since you have
a wall separating the second room from
the first room so therefore light
doesn't enter the second room at all so
so the second room is completely down
right so he explained that since light
travels in a straight line whenever you
have an obstruction or a wall in between
light doesn't pass through that wall
this shows that light always travels in
a straight line it gets obstructed and
it cannot move in a curved path so these
are some of the things which Newton
explained and he tried to convince
people with his explanation and people
also got convinced and the particle
theory of light came into picture
so people accepted the particle nature
of light people accepted that light is
nothing but it is a form of energy but
it is made up of a huge number of small
small particles right now while
explaining now this is how he explained
it in front of the public and they all
accepted it because for them Newton was
a big name and they respected him so
everybody accepted the skill but if you
look at the explanation which means
which he gave for the phenomenon of
refraction
there was a major flaw which Newton did
not project Newton knew that this flaw
was there but still he did not emphasize
much on that part so what was that
Newton told as I explained just now that
when the particle
from a rarer medium to a denser medium
the corpuscles are the light particles
they get accelerated what do I mean by
accelerated that means their velocity
increases so that would mean that this
velocity V 2 in the denser medium will
be greater than the velocity V 1 in the
rarer medium like so that means
according to Newton's explanation
velocity of the corpuscles in denser
medium should be greater than the
velocity in really medium which in turn
means that the velocity of night in
denser medium is greater than the
velocity of light in either a medium
right but later it was proved that this
was not correct so this was a major flaw
in his explanation but Newton never
emphasized much on the velocity he just
told that since light particles are
coming in it is getting attracted so it
bends towards the normal he kind of
ignored the velocity part right so now
so this is what Newton told and people
accepted but this was not the truth
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