Atmospheric Refraction - Human Eye, CBSE Class 10 Physics Video Lecture

hello friends this video on human eye
and the colorful world park7
is brought to you by exam for calm you
move here from exam please make sure
that you have watched all the videos for
part 6
before going ahead with part 7 so with
this we will conclude our topic on none
rainbow and now we will look at
something called atmospheric refraction
so here we will see some of the
phenomenon of atmosphere which happens
as a result of refraction some of the
very interesting phenomenon which we see
in our day-to-day life but we never knew
that it happens because of refraction
the first one is the printing of the
stamps all the first see the stars
twinkling at night but what makes the
star strength and have we ever thought
of that maybe yes maybe no let to let
you know that twinkling of stars is due
to the phenomenon of refraction of light
so it states bits because of refraction
what happens that means the stars
twinkle in this case let the stars are
several miles away from them but they
are far away from us so the light which
is coming from the stars and stars have
got their own light right so this light
of the star when it reaches our eyes it
comes across so many things it comes it
comes across the atmosphere as well and
this atmosphere consists of several
particles like I mean we in that most
layer you have so many things right
and the because of the presence of so
many things the atmosphere has got a
different refractive index now when this
light passes through so many layers of
the atmosphere before reaching our eye
what happens refraction takes place
because it keeps entering from one
medium to another medium now because of
this refraction what happens there is a
shift in the
position as I mentioned before also
right remember the topic on refraction
through a glass slab what happens a
lateral shift takes place that means
when refraction happens there is a
lateral shift of the convergent ray from
the incident ray that means the Ray
which enters our eye is gets laterally
shifted from the actual position of the
object now in this case since the
refraction occurs several times for
example when this ray enters from this
medium to this medium refraction takes
place right so maybe the emergent ray
reaches your eye here so you feel that
the object is here now again in this
particular day it is entering from this
medium to this medium again refraction
is taking place as a result maybe the
Ray which is reaching your eye it is
here so you feel along the line of sight
of this emergent ray that the object is
here again it enters the other medium so
since the number of refraction which is
experienced by the light is too many so
to many times refraction takes place so
therefore we are able to see too many
apparent position of the stars now
so sometimes we see that the star is
here again we see the star is not a like
too many happening position means let us
suppose at one instant we see that the
star is here in the next instant we see
that the star is here again on the next
instant we see the star is here again on
the next instant we see that the star is
here so then what happens this effect is
seen like twinkling that means sometimes
you see a star here sometimes here
sometimes here sometimes here since all
these positions are very nearby so this
effect is actually seen as twinkling of
the stars so twinkling of stars is
nothing else it happens because of
multiple refraction which is experienced
by the light to reach from the stars to
the eye when it crosses so many layers
of atmosphere and whenever refraction
takes place there is a lateral shift
involved because of which we never view
the actual position of the object
instead we are able to view the apparent
position of the object so similarly
there is another
atmospheric phenomenon which we see and
which is because of diffraction that is
advance sunrise and delayed sunset
Santa's always visible to us two minutes
before the actual sunrise and two
minutes after the actual sunset because
of atmospheric refraction now what does
atmospheric refraction you understand
atmospheric refraction is nothing but
the refraction which takes place because
of the different refractive in basis of
the atmosphere because of the presence
of atmosphere when refraction takes
place we call it as atmospheric
refraction now what is sunrise when
sunrise takes place as the Sun right
this is later suppose if this is the
horizon
so whenever the Sun comes above this
horizon we see that sunrise has taken
place whenever Sun goes below this
horizon we say that sunset has taken
place so why does it happen that even
before the actual sunrise day place we
are able to view the Sun that is again
because of diffraction what happens let
us suppose right now the Sun is here
that means the sunrise has not yet taken
place so the Sun is here now the light
rays from this Sun reaches our eye
crossing the layers of the atmosphere
during which refraction of light takes
place therefore the light ray which
finally reaches your eye after all
refraction is somewhat like this it gets
bent here and there and then again the
light which reaches your eye you see
along the line of sight of that emergent
ray so as for your line of sight you are
able to see the Sun somewhere here right
so even though the Sun is here but you
are able to see the Sun to be here that
means right now as the Sun rises taking
place actually no but are you able to
see the Sun above horizon yes so that
means what it for you sunrises taking
these so that is why we are able to view
the Sun two minutes before the actual
sunrise takes place similarly the same
thing happens for sunset also after the
Sun goes inside I mean it goes below the
horizon
actually sunset has taken place but
still when the race reaches our eye it
reaches in such a way that we are able
to see the Sun here that means we are
still able to see the Sun that means
even after actual sunset has taken place
we can still see the Sun for another two
minutes so this advanced sunrise and
delayed sunset is because of the
phenomenon of atmospheric refraction
thank you please visit exam few calm to
watch free educational videos try free
online tests get the best quality study
materials study from the best tutors and
mentors and much more thank you once
again