L8 : Shadow Formation - Light Shadow & Reflection, Science, Class 6 Video Lecture

hello friends this video on light
shadows and reflection part 8 is brought
to you by example calm no more fear from
exam now we have been talking about
images we have been talking about
reflection but having ever noticed that
with a lot of objects images are not
formed rather shadows are formed so
anyway these objects are placed in
presence of light you see a black shadow
being formed of that object so what is
this shadow and how are the shadow is
formed so let's see what is shadow
well shadow is nothing but a space where
light is blocked by an opaque object so
whenever you have an object which
doesn't allow light to pass through it
so what will happen some space will get
blocked by that object so let's look at
this banner so this pillar is blocking
light so light is able to pass through
all these areas but only this portion is
blocking light and that is why lamp is
not able to reach only this part so this
part remains dark and that that part is
seen as a shadow so shadow is not an
object shadow is not an image it is just
that part where light could not reach it
light could not reach because it was
blocked by an opaque object now shadows
are also formed by translucent objects
because translucent objects also
partially allows light to pass through
them so some part of the light is also
blocked by translucent objects but the
image is formed by opaque objects are
more clear and move this thing so when
we you stand in the Sun you are able to
see your shadow so how do you should see
that shadow because our body is opaque
we do not allow light to pass through us
that's why we are not transparent and
that is why a shadow is formed behind us
and if you look at the shape of this add
shadow it is quite similar to our shape
because the shape of our body is not
allowing light to pass so only for that
shape there is darkness behind and
that's how shadow is formed so this
shows that transparent objects can never
form shadows because they allow light to
pass through them so there will be no
dark area
behind them now the question is how
exactly is a shadow form now for shadow
to form two things are absolutely
important light has to be present in
dark shadows are not formed and opaque
or translucent object has to be present
because if there is no object to block
light again shadows will not be formed
so let us look at this example
so here light falls on this object from
the front that is light falls on this
person from front okay so only the shape
of this person doesn't allow light to
pass through it that is why you see that
same portion as dark because light
couldn't reach here and that is why
shadow is falling now let us say if we
take a torch and provide light from this
direction over the shadow what will
happen when you still see the shadow you
will not be able to see shadow because
now light is able to reach this portion
as well
so therefore shadows will only be formed
in that area where there is no light
where light could not reach due to the
presence of an opaque object so if you
have light coming from this direction as
well as this direction no shadow will be
formed so even though an opaque object
is present in presence of light shadows
will not be formed because there is no
such area where light is completely
blocked by an optic object so maybe this
area light is blocked by this object but
when this side light is able to reach
here so shadows will not be formed so
shadows are basically the dark areas
where light doesn't reach now if instead
of this person if you replace this
person with a glass slab no shadow will
be formed because through glass slab
light will be able to pass through it so
there may be no dark region behind now
when you look at the shapes of shadows
you will observe a lot of interesting
stuffs so let's say if you think of a
ball of what is the shape of a ball it's
a sphere but when you look at the shower
that is being formed by the ball they
like what you are seeing right now on
the screen do you see a sphere the
anyway and I talked about the shape of
the shadow it's not a sphere
it looks like an ellipse so it is not
necessary that the shape of the shadow
will be identical to the shape of the
object look at this box so the shape of
the box is like a kind of cuboid but
when you look at the shadow shadow is
just a rectangle that's because when
light is being provided light is coming
from this direction so only this part of
the box is not allowing light to pass
through it so that is why only this
portion is that because light is not
able to reach here and that's why the
shape of the shadow is a rectangle
similarly if light was falling from this
phase of the box the shadow would have
formed on the other side so basically it
is this what will be the shape of the
shadow that is determined by the
direction in which light is falling on
that object it is also determined by the
shape of the object and it is also
determined which phase from which angle
are you looking at them shattered so
there are various factors on which the
shape of the shadow is dependent you
look at this car so the shadow which you
should see here is just kind of a
rectangle however the shape of the car
is very much different that's because
maybe light is falling from the top of
the car that is why this bottom part is
that area where light is being blocked
by this entire base of the car so that
is why the images like that you had this
grasshopper so when you look at its
shadow you see it is very much different
from the real picture of the grasshopper
so shadow moving into that area where
light is not able to reach think of this
flower box you can get many different
shapes of shadows of the same flower box
just by changing the direction of light
falling on the bus so right now the
light is falling in from this direction
that is why you should see a shadow here
if light falls on this direction that
the shadow will be formed here if light
falls on this group front the shadow
will be formed at the back so basically
depending on the direction from which
light is incident on that object also it
determines where the shadow will be
formed and what will be the shape of
those shadows so when we talk about
shape of shadows we see a lot of
interesting shadows which are being
formed with our hands in fact a lot of
people know this beautiful art of making
animals with their hands making
different postures with their hands and
when you look at their shadows they look
they look like some animals you look at
this just with his two hands he is able
to make a shadow which resembles a
rabbit look at this with two hands he is
able to make something which looks like
a flying bird so that's how you know a
lot of animals are being shown with
their shadow so this is another
interesting stuff so basically any
object the shape of the object doesn't
necessarily tell us what will be the
shape of this shadow so with one
particular object you can have multiple
shapes of shadows for example if you
talk about cylinder if the light falls
on one surface you might get a
rectangular shadow if light falls on
some other side you might get a circle
as a shadow so it depends the on the
orientation of the incident light also
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