Overview of Image formations by concave and Convex Mirrors Video Lecture - Class 7

hello friends this video on light part
11 is brought to you by exam for calm no
more fear from exam so let us now look
at the image formation by concave mirror
in detail so we will see how different
types of images are formed by a concave
mirror so just to remind you what is
concave cave means something which goes
inside so the inside surface is going to
be the mirror so your object is going to
be somewhere here so this is how the
concave mirror would look like so let's
say this is your concave mirror and this
is your I'm sorry this is your concave
mirror as you can see here so this is
your on cave mirror and this is your
object and this is the image now you
might ask that why are we seeing the
image here because what kind of image is
formed here if you see the object is
also on this side of the mirror the
image is also formed on the same side so
that's the speciality here right so
since the object and the image both are
formed on the same side of the mirror so
we can actually get this image on the
screen so basically you can try this
experiment out in your home or in your
laboratory wherever you have a concave
mirror available so with that concave
mirror you place an object so here I've
placed a flower bus at a considerable
distance from the mirror and then you
put a screen on the same side of the
mirror so that screen could be anything
it could be a piece of clothes or it
could be a sheet of paper you just have
that screen there and you will see that
you will be able to see the image there
and the image would be diminished that
is it is smaller in size than the object
so if you see here image is smaller and
the image is also inverted so you see
that that's quite evident that the image
is inverted now we will start seeing the
magic of the concave mirror you know
when when we start changing the position
of the object so now what we have
is so what we do is we try to change the
distance of the object from the barren
so for that what you can do is you can
either change and you can either move
the object from one position to other or
you can also change the position of the
screen because as you move the screen
also so effectively the distance between
distance of the image from the mirror
changes which in turn changes the object
distance also from the middle because
entire calculation changes now we are
not getting into the calculations at
this level what I am trying to show is
as the distance changes as the position
changes the type of image also changes
so here we observe that when the object
is brought even more closer to the
mirror the image is still inverted but
now the images of the same size as that
of the object and do you know what is
this position of the object now at this
point of time I already gave you a brief
introduction of different terms related
to a spherical mirror so I spoke about
the center of Carnation you remember see
the center of curvature is that is the
center of the sphere from which that
middle is being derived so when this
object is located at the center of
curvature of this mirror so the center
of curvature this mirror is like we're
seeing it from the backside right so
this middle will have some centre of
curvature which will be somewhere here
and when the object is placed at the
center of curvature at that time the
image which is formed is of the same
size but it is inverted right now what
we do we try to bring the object even
more closure and gradually we see that
now we are getting an enlarged image so
instead of same size now the images
become all the more magnified so the
image is bigger than the size of the
object and if we even try to bring it
very close to the middle
if you pray you bring the object
extremely close to the mirror what do
what do you observe so now you do not
see the screen here you know why because
in this case the object is on this side
the image is on the other side of the
middle in this case this is the mirror
so object is on this side of the mirror
image is also on this side of the mirror
so both are on the same sides so you you
will be able to get the image on the
screen but when the image is formed on
the other side of the mirror like how it
happens when we stand in front of the
dressing-table we cannot get our image
on the screen so the same thing happens
here so basically with the object is
brought extremely close to the concave
mirror the image that is form that is
erect so you see you see an erect image
however you are not able to see the
entire image of the object that's
because the image is enlarged so the
image is highly magnified so you are
only able to see some part of the image
because the mirror is not that big
correct so what did we observe we
observe that with a concave mirror with
the same object you can get enlarged
image you can get a diminished image you
can get image of the same size as that
of the object you can get inverted image
you can get edit image and all these
changes with the position of the object
from the mirror so basically these are
very simple experiments in fact these
are just observations so if you have a
concave mirror near you you can try this
these out yourselves so which we help
you to know that okay so that's the
beauty of spherical mirrors and because
of this property this variable mirrors
are used in a wide variety of
applications so overall if you will look
at all the four scenarios that we
discussed we saw that at a certain
position of the object the image was
diminished inverted then gradually it
became of the same size still inverted
then it became enlarged still inverted
and finally it became erect and enlarged
so can you tell me based on whatever I
have explained before can you tell me in
which of these scenarios the image is
real and in which
the scenarios the image is virtual now
what is a real image I told you that
real images formed when they reflected
it is actually meat and a virtual image
is formed when the reflected rays appear
to mate so that is the basic way to
define real image and put virtual image
but what are the other ways to identify
which image is real image and which
image is virtual so another way is
whenever you have a real image so that
real image can always be obtained on the
screen because the real image is always
formed on the same side as that of the
object because the reflected rays are
actually moving so when they are
actually meeting that means they are
meeting on the same side as that of the
object now in all of these cases you see
the images are formed on the same side
of the object and that is why we are
able to get them on the screen so these
are all real images however in this case
the image cannot be obtained on the
screen because it has formed on the
other side of the mirror and it it is
formed on the other side because there
is did not meet actually so we just we
just assume that if we try to meet them
try to make them meet somehow using
dotted lines so they will be able to
meet somewhere on the other side of the
mirror so this is the scenario where a
virtual image is formed so I hope that
the concept of real image virtual image
all these things should be very clear
because this is where from where you
start learning the basics of optics so
as you put your senior classes you will
study about these named things but in
more detail so let's have a quick review
of image formation by concave mirrors so
here you see we have made a list of
object location where now these are the
points where the object will be located
so these are the point places where the
image will be formed and what type of
image will be formed and what would be
the size of the image now when you go to
your senior classes you will actually
calculate and see that how the images
are formed at these locations so that is
not required at this level
however we
have we you can always verify this table
with the observations like whatever we
discussed in the last two slides so when
the object is located at infinity when
the object is very far away from the
mirror then the image is formed at the
principal focus and the image is real
inverted and it is smaller in size now
when the object is beyond the centre of
curvature so it is like let's let's say
let's take a mirror like this let's say
this is the mirror
so this is our concave mirror okay and
this is the principal axis of the mirror
let's say this is them pull this is the
focus and let's call this as the center
of curvature so in the first scenario we
assume that the object is like at
infinity somewhere very far so in that
case the image will be formed at the
focus here so the image is formed here
because the reflected rays which
actually meet at this point now when the
object is beyond see somewhere here if
this is where the object is then the
image will be formed somewhere between C
and F and here also the image would be
inverted small in size and of course
real because they are the same side of
the mirror when the object is at C at
this point then the image will also be
formed at the center of curvature but
this would be inverted and it will be
same size as that of the object so you
see as the object is coming closer to
the mirror the size of the image is
actually increasing you see the object
is gradually coming closer from infinity
to beyond center of curvature to centre
of curvature so now we say that object
is between centre of curvature and focus
so in that case the image is formed
beyond the centre of curvature but here
the image is gradually increasing in
size so as we are going down the object
is coming closer to the middle and the
size of the object is gradually
increasing and finally when we reach
between focus and fold so when the
object is somewhere here then the image
that is formed is enlarged and it is
formed on the earth
of the mirror so something like this
would be formed on the other side of the
mirror so this is the like the overview
of how different images are formed in
concave mirrors when the objects and the
object is located at different places so
in a similar way it will look at the
image formation by convex mirror now in
convex mirror what happens it is a
diverging mirror so in this case we
observe that all these erect and
diminished images are formed
irrespective of the location of the
object so this also you can tie out on
your own now even if you keep changing
the position of the object take it to
infinity bring it very close to the
mirror so every time you will see a
direct image and every time you will see
a diminished image that is an image
which is smaller in size and can you
tell me what kind of image is this real
or virtual of course virtual why because
the image is formed on the other side of
the mirror right so this is a virtual
image so basically a convex mirror is
used in all those places where we need a
diminished image so variable we need a
smaller image of an image which is
smaller in size as that of compared to
the object so there we will use one next
mirror because the convex mirror doesn't
matter where the object is located every
time it will give an erect and
diminished image so now can you guess
the what kind what kind of spherical
mirror it is used in the real view
mirrors of your car because that
rearview mirror gives a view of the
entire scene at the background so even
if a huge truck is standing at behind
your car you will be able to see that
entire trunk in that small mirror how
are you able to see it because a
diminished image is being formed in the
barrel so I am pretty sure that you must
have been able to guess which type of
ladle is present in the rear back view
mirrors of your heart so this is how you
need to learn so now try observing
different types of mirrors which you see
around yourself and by observing the
type of images which are produced by
those mirrors you can
guess what kind of mirror is that so
basically if we quickly review the image
formation of convex mirrors we see that
okay
the variable the object is located does
not matter whether the object is located
at infinity which is very far or
anywhere between the pole and the
Infinity whether at the center of
curvature or the focus or between focus
and pole doesn't matter wherever it is
located so every time the image would be
virtual and erect and every time the
image would be diminished it is just
that if the image is going far away the
image will keep becoming all the more
diminished so that's why you see if the
object is at infinity then the image
will be highly diminished and if the
object is quite near even then the image
is going to be diminished but
comparatively less diminished but every
time you will get a diminished virtual
and erect image with a convex mirror
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