CBSE Class 10 > Class 10 Videos > Image Formation by Eye - Human Eye, CBSE Class 10 Physics
Image Formation by Eye - Human Eye, CBSE Class 10 Physics Video Lecture
FAQs on Image Formation by Eye - Human Eye, CBSE Class 10 Physics
| 1. What is the human eye? |  |
Ans. The human eye is a complex organ that allows us to perceive and interpret visual information from our surroundings. It plays a crucial role in our sense of sight.
| 2. How does the human eye form an image? | |
Ans. The human eye forms an image through a process called refraction. Light from an object enters the eye through the cornea, passes through the pupil, and is focused by the lens onto the retina at the back of the eye. The retina then converts the light into electrical signals that are sent to the brain for interpretation.
| 3. What is the role of the cornea in the formation of an image? | |
Ans. The cornea is the transparent outermost layer of the eye. It acts as a protective covering and also helps in focusing light onto the retina. It helps in the initial bending of light rays and accounts for most of the eye's refractive power.
| 4. How does the lens contribute to image formation in the human eye? | |
Ans. The lens in the human eye plays a crucial role in focusing light onto the retina. It is a flexible and transparent structure that can change its shape to adjust the focal length. By changing its shape, the lens ensures that the image formed on the retina is clear and sharp.
| 5. What is the significance of the retina in the human eye? | |
Ans. The retina is a layer of tissue at the back of the eye that contains photoreceptor cells called rods and cones. These cells convert light into electrical signals, which are then transmitted to the brain via the optic nerve. The retina is responsible for the initial processing of visual information and plays a vital role in our ability to see and perceive the world around us.
Text Transcript from Video
hello friends this video on human eye
and colorful world part 2 is brought to
you by exampie or calm no more fear from
exam let us now try to understand how
exactly image is formed by the eye what
we already learnt the different parts of
the eye so we know that we have a eye
lens but let's see how exactly where
exactly the image was formed by the eye
lens
now the image always has to be formed on
the retina now why is that so now that's
because retina is the screen for our
eyes like how we have now normally when
we learnt about the image formation by
lenses we saw that we always had a lens
we had an object and we had a screen and
the image is formed on the screen that's
how the normal scenario works with a
convex lens now for our eye also we have
the eye lens in place and we have this
ready now which acts as the screen where
the image has to be formed
now we have to ensure that every time
the image is formed on the retina now
since we have a convex lens now what
happens is the image that is formed on
the retina that is the screen is an
inverted image we already learned that
convex lens swelling the image is
considerably away most of the time image
produces real inverted image now you
might ask that okay if we are inverted
image is formed on the retina then how
do we see things in it that's because
our brain then interprets that inverted
image as an erect image so the entire
process of seeing an object not only
depends on our eyes but also on our
drink so brain plays a very important
role when we see things so every time we
need to ensure doesn't matter very good
the object is but the image always has
to be formed on the retina
now object can be anywhere object can be
far object can be mirror so how do we
ensure that the image is always on the
retina so let us have a look at that so
for that what we do is we change the
the length of the lens because we cannot
change the object distance let's say I
want to see a tree and the trees is far
away from me so I cannot drink that tree
near me and then see it we can't do that
so object distance is not under our
control okay
image distance is also not under our
control it was recognized at the fixed
please and the image has to be found on
the retina so what is under our control
the lens now if somehow we can change
the focal length of the lens in that
case the position where the image is
formed and also recorder so if the image
is very far away or if the image is
quite close depending on the distance of
the so if the object is very far away or
the object is very close depending on
the position of the object we can alter
the focal length of the eye lens so that
the image is always formed on the retina
so that is the concept that is used
inside our eye so let us try to
understand in more detail so let us say
we are trying to see a nearby object so
let us say this is the object that we
are trying to see now this is our lens
now what do we know from our basic
knowledge on the three diagrams a ray of
light passing parallel to the principal
axis
what happens after passing through the
lens it would pass through the focus of
the lens right now let us say this is
the principal focus for this lens so
after that it passes through the focus
and the ray of light which passes
through the optical center of the lens
that moves straight after refraction and
then these two rays they meet at this
point where an inverted image is formed
so that is how image formation is taking
place right now and this is our retina
this part is the retina which is the
screen so perfect in this case when I am
seeing a nearby object things are
working absolutely fine now if the
object is not located quite close and it
is located far away in that case what
would happen now if the object is very
far away as per our knowledge on lens we
know that when an object is
very far away from a context lens let's
say this is convex lenss where the
object is far away the rays would be
coming parallel from that object and
after refraction they will meet at a
point and that point is the principal
focus so this is when the object is at
infinity so in this case also if we want
to view an object which is far away and
if we assume that the lens will remain
like this in that case where in the
image we found the image will be formed
here at the principal focus because
their rays after passing through the
lens will meet at the principal focus
but that would not satisfy our criteria
because we want the image to be formed
on this screen now for image to be
formed on the screen the principal focus
should lie on the screen so when the
focus is lying on the screen then it
should be fine
so what do we do when you are viewing a
very far of object we change the focal
length of the lens now how we change the
focal length of the lens by changing its
width here you see a fat lens if you
look at the thickness of the lens
you see a fat lens but here when you
look at the thickness it is
comparatively a thin lens now with the
thickness of the lens changes it focal
length also changes how let us try to
understand let's see you have a lens
like this which is almost straight so
that means if it is almost like very
little curve what does that mean that
means it is part of a circle which is
quite big right so this circle will have
the radius somewhat like this so this
would be the focal length this distance
would be the focal length now let us say
you have a lens which is like very much
curved like this so in this case if the
Glens has more curve that means this is
part of a smaller sphere therefore for
this the radius of curvature would be
less and therefore the focal length be
lesser so whenever you have a fat lens a
fat lens will always have
lesser focal lengths so fat lengths
means less focal length and thin lens
would always mean more focal length now
here if we are able to make the lens
shimmer in that piece its focal length
will increase so earlier the focal
length was somewhere here now the focal
length increased and the focus shifted
to somewhere here so in this case what
happened the rays of light parallel rays
of light came from an object which is
far away and after passing through the
lens
they met at the focus and where is the
focus that is on the retina so the image
is formed on the retina so you see if we
are able to change the thickness of the
lens then we are able to ensure that
whether the object is here or the object
is far away we will always get the image
on the retina so now our next challenge
is how do we ensure or who will take
care of the fact that the thickness of
the lens will change depending on the
location of the object how will we
change the thickness of the lens so let
me see so who all tells the thickness of
the eye lens now that is done by the
ciliary muscles now if you know that the
structure of the eye very closely this
is the lens so this one is the lens the
lens is connected to the cirrie muscles
here so here you have the ciliary
muscles and you have these muscles on
both end of the lens so these are also
ciliary muscles these are also ciliary
muscles now the ciliary muscles and the
lens they are connected via certain
ligaments which are called suspensory
ligaments so here you have the ciliary
muscles here and then you have these
ligaments here and then it connects to
the lens similarly here you have the
ligament here and this side you have the
ciliary muscles now as we know that
muscles are always capable of
contracting so washers can contract
muscles can relax now as the muscles
contract or relax what would happen the
corresponding ligaments will also move
and as the ligaments move this can
impact the thickness of the lens because
if the ligaments they get stretched let
us see the ligaments get stretched this
side the sector one will have a little
try to stretch the lens from both sides
and that is the lens will tend to become
thinner because somebody is trying to
push the lens from this side somebody's
trying to push the lens from this edge
it'll become clearer but when the
ligaments are kind of relaxing when the
ligaments are set free then the lens
will also be set free nobody is pushing
it from anywhere and the lens will
become a fad lens so this is how we will
be able to control the thickness of the
lens
now when the object is nearby what
happens is the ciliary muscles contract
now when the Sirian muscles contract now
these muscles contract that means what
happens the muscles are contracting
therefore these ligaments which are
connected to the muscles these ligaments
slack and they are like set free because
of which nobody is trying to push this
lens so the lens is also very free
nobody is pushing it so the lens is like
taking old it's all its space and it is
like thickened enough it is a fact lens
and when the lens is fat it has a lesser
focal length and therefore focal length
is only two here so this would be the
focal length in this case and that's how
we are able to see the image the image
is formed on the retina now what happens
when the object is far away the moment
the object is far away these serious
muscles will expand
now when the ciliary muscles expand what
happens the ciliary muscles take a lot
of space because they have now expanded
now when they take a lot of space what
happens to these ligaments now they have
taken a lot of space nor thus ligaments
tend to make some space for itself so it
kind of get stretched now when it gets
stretched it stretches the lens also
from both ends now when somebody is
pushing the lens from both the sides
like it is something like you are
sitting somewhere and somebody is
pushing you from the side from below
from that side of what will happen you
won't be able to sit comfortably you did
end up stretched from both sides that is
happening with the lens the lens is
stretched on both sides sight is
becoming thinner so the lens is thin and
as a result it has increased focal
length so now you the principal focus
gets shifted here so this is the focal
length now so you see the same length it
is just that the lens was set free so it
was a fat lens with a lesser focal
length now the lens is kind of stretched
by the stretch set suspensory ligaments
because of this it is a thin lens with
an increased focal length so I hope this
concept is clear that how ciliary
muscles control the focal length of the
idents because
controlling the focal length is very
important otherwise we will not be able
to make an image form on the retina and
the image formation doesn't happen on
retina we will not be able to see
anything so now here we introduce a term
watt power of a combination so power of
accomodation is the ability of the eye
lens to adjust its focal length to see
both distant and close objects now as we
said that the lens and become fat the
lens can become thin but there is a
limitation to that also now there has to
be a certain limit up to which it can
become thin similarly there has to be a
certain limit up to which it can become
thick so that ability or that
flexibility of the islands is what we
call power of accomodation that means
how much the lens can accommodate how
much the lens can adjust to ensure that
the image is formed on the retina so as
we saw that these are like the two
extreme conditions where the thickness
of the lens changes now the closest
distance of an object for which the lens
can focus the light on the retina that
is known as the least distance of
distinct vision now if you have ever
observed it for yourself that if you
take a book and bring it extremely close
to your eyes will you be able to
the book you can't if you haven't read
it here try it now bring the book
extremely close to your eyes almost
touching your eyes you don't be able to
read the book No so when the book is so
near to you that time also you can't
read it because now the distance of the
object has reduced so much that the lens
is not able to you know adjust its focal
length so much to produce an image of
the retina so the image is not being
formed on the retina so there is a
minimum distance minimum distance of the
object for which their lens can focus
the image on retina so that distance is
called least distance of distinct vision
that means that is the minimum distance
at which you can very distinctly see
that object and this distance is also
known as the near point that point where
the object should be located that point
is termed as the near point and for a
normal eye that near point is 25
centimeters so if you place any object
if you place a book at a distance of 25
centimeters from your eye you will be
able to read it very comfortably but if
you bring it maybe some to a distance of
10 centimeters from your eyes you will
not be able to read it clearly
however this value of near point often
increases with age because as a person
ages the ability of the lens or the
power of accommodation of the lens
reduces the lenses no more that flexible
as a result you would have seen that
elderly people often bring a book you
know they really need to see it very
closely to be did otherwise they they do
not get to read it very properly so this
the value tend to increase at with age
so for a normal eye the near point is 25
centimeters at the far point is infinity
that means the fire point can be
anywhere because we already saw in the
ray diagram that if the object is far
away even if the object is at infinity
the lens can adjust itself in such a way
that the image is formed on the
principle focus and the fluid
focus lies on the retina so fire point
could be infinity but the near point has
to be 25 centimeters so with this
figured an idea that about how our eyes
reduce images of objects and then how
our brain interprets those images so
that we can see the objects as they are
thank you please visit exam fee or comm
for free quality education you can learn
with a simple four-step learning process
wherein you can watch video lessons you
can ask your questions you can refer
notes and you can take a free online
test we have content for class 6 to 12
on physics chemistry mathematics and
biology along with practical videos so
please subscribe to our channel for
daily updates thank you
and colorful world part 2 is brought to
you by exampie or calm no more fear from
exam let us now try to understand how
exactly image is formed by the eye what
we already learnt the different parts of
the eye so we know that we have a eye
lens but let's see how exactly where
exactly the image was formed by the eye
lens
now the image always has to be formed on
the retina now why is that so now that's
because retina is the screen for our
eyes like how we have now normally when
we learnt about the image formation by
lenses we saw that we always had a lens
we had an object and we had a screen and
the image is formed on the screen that's
how the normal scenario works with a
convex lens now for our eye also we have
the eye lens in place and we have this
ready now which acts as the screen where
the image has to be formed
now we have to ensure that every time
the image is formed on the retina now
since we have a convex lens now what
happens is the image that is formed on
the retina that is the screen is an
inverted image we already learned that
convex lens swelling the image is
considerably away most of the time image
produces real inverted image now you
might ask that okay if we are inverted
image is formed on the retina then how
do we see things in it that's because
our brain then interprets that inverted
image as an erect image so the entire
process of seeing an object not only
depends on our eyes but also on our
drink so brain plays a very important
role when we see things so every time we
need to ensure doesn't matter very good
the object is but the image always has
to be formed on the retina
now object can be anywhere object can be
far object can be mirror so how do we
ensure that the image is always on the
retina so let us have a look at that so
for that what we do is we change the
the length of the lens because we cannot
change the object distance let's say I
want to see a tree and the trees is far
away from me so I cannot drink that tree
near me and then see it we can't do that
so object distance is not under our
control okay
image distance is also not under our
control it was recognized at the fixed
please and the image has to be found on
the retina so what is under our control
the lens now if somehow we can change
the focal length of the lens in that
case the position where the image is
formed and also recorder so if the image
is very far away or if the image is
quite close depending on the distance of
the so if the object is very far away or
the object is very close depending on
the position of the object we can alter
the focal length of the eye lens so that
the image is always formed on the retina
so that is the concept that is used
inside our eye so let us try to
understand in more detail so let us say
we are trying to see a nearby object so
let us say this is the object that we
are trying to see now this is our lens
now what do we know from our basic
knowledge on the three diagrams a ray of
light passing parallel to the principal
axis
what happens after passing through the
lens it would pass through the focus of
the lens right now let us say this is
the principal focus for this lens so
after that it passes through the focus
and the ray of light which passes
through the optical center of the lens
that moves straight after refraction and
then these two rays they meet at this
point where an inverted image is formed
so that is how image formation is taking
place right now and this is our retina
this part is the retina which is the
screen so perfect in this case when I am
seeing a nearby object things are
working absolutely fine now if the
object is not located quite close and it
is located far away in that case what
would happen now if the object is very
far away as per our knowledge on lens we
know that when an object is
very far away from a context lens let's
say this is convex lenss where the
object is far away the rays would be
coming parallel from that object and
after refraction they will meet at a
point and that point is the principal
focus so this is when the object is at
infinity so in this case also if we want
to view an object which is far away and
if we assume that the lens will remain
like this in that case where in the
image we found the image will be formed
here at the principal focus because
their rays after passing through the
lens will meet at the principal focus
but that would not satisfy our criteria
because we want the image to be formed
on this screen now for image to be
formed on the screen the principal focus
should lie on the screen so when the
focus is lying on the screen then it
should be fine
so what do we do when you are viewing a
very far of object we change the focal
length of the lens now how we change the
focal length of the lens by changing its
width here you see a fat lens if you
look at the thickness of the lens
you see a fat lens but here when you
look at the thickness it is
comparatively a thin lens now with the
thickness of the lens changes it focal
length also changes how let us try to
understand let's see you have a lens
like this which is almost straight so
that means if it is almost like very
little curve what does that mean that
means it is part of a circle which is
quite big right so this circle will have
the radius somewhat like this so this
would be the focal length this distance
would be the focal length now let us say
you have a lens which is like very much
curved like this so in this case if the
Glens has more curve that means this is
part of a smaller sphere therefore for
this the radius of curvature would be
less and therefore the focal length be
lesser so whenever you have a fat lens a
fat lens will always have
lesser focal lengths so fat lengths
means less focal length and thin lens
would always mean more focal length now
here if we are able to make the lens
shimmer in that piece its focal length
will increase so earlier the focal
length was somewhere here now the focal
length increased and the focus shifted
to somewhere here so in this case what
happened the rays of light parallel rays
of light came from an object which is
far away and after passing through the
lens
they met at the focus and where is the
focus that is on the retina so the image
is formed on the retina so you see if we
are able to change the thickness of the
lens then we are able to ensure that
whether the object is here or the object
is far away we will always get the image
on the retina so now our next challenge
is how do we ensure or who will take
care of the fact that the thickness of
the lens will change depending on the
location of the object how will we
change the thickness of the lens so let
me see so who all tells the thickness of
the eye lens now that is done by the
ciliary muscles now if you know that the
structure of the eye very closely this
is the lens so this one is the lens the
lens is connected to the cirrie muscles
here so here you have the ciliary
muscles and you have these muscles on
both end of the lens so these are also
ciliary muscles these are also ciliary
muscles now the ciliary muscles and the
lens they are connected via certain
ligaments which are called suspensory
ligaments so here you have the ciliary
muscles here and then you have these
ligaments here and then it connects to
the lens similarly here you have the
ligament here and this side you have the
ciliary muscles now as we know that
muscles are always capable of
contracting so washers can contract
muscles can relax now as the muscles
contract or relax what would happen the
corresponding ligaments will also move
and as the ligaments move this can
impact the thickness of the lens because
if the ligaments they get stretched let
us see the ligaments get stretched this
side the sector one will have a little
try to stretch the lens from both sides
and that is the lens will tend to become
thinner because somebody is trying to
push the lens from this side somebody's
trying to push the lens from this edge
it'll become clearer but when the
ligaments are kind of relaxing when the
ligaments are set free then the lens
will also be set free nobody is pushing
it from anywhere and the lens will
become a fad lens so this is how we will
be able to control the thickness of the
lens
now when the object is nearby what
happens is the ciliary muscles contract
now when the Sirian muscles contract now
these muscles contract that means what
happens the muscles are contracting
therefore these ligaments which are
connected to the muscles these ligaments
slack and they are like set free because
of which nobody is trying to push this
lens so the lens is also very free
nobody is pushing it so the lens is like
taking old it's all its space and it is
like thickened enough it is a fact lens
and when the lens is fat it has a lesser
focal length and therefore focal length
is only two here so this would be the
focal length in this case and that's how
we are able to see the image the image
is formed on the retina now what happens
when the object is far away the moment
the object is far away these serious
muscles will expand
now when the ciliary muscles expand what
happens the ciliary muscles take a lot
of space because they have now expanded
now when they take a lot of space what
happens to these ligaments now they have
taken a lot of space nor thus ligaments
tend to make some space for itself so it
kind of get stretched now when it gets
stretched it stretches the lens also
from both ends now when somebody is
pushing the lens from both the sides
like it is something like you are
sitting somewhere and somebody is
pushing you from the side from below
from that side of what will happen you
won't be able to sit comfortably you did
end up stretched from both sides that is
happening with the lens the lens is
stretched on both sides sight is
becoming thinner so the lens is thin and
as a result it has increased focal
length so now you the principal focus
gets shifted here so this is the focal
length now so you see the same length it
is just that the lens was set free so it
was a fat lens with a lesser focal
length now the lens is kind of stretched
by the stretch set suspensory ligaments
because of this it is a thin lens with
an increased focal length so I hope this
concept is clear that how ciliary
muscles control the focal length of the
idents because
controlling the focal length is very
important otherwise we will not be able
to make an image form on the retina and
the image formation doesn't happen on
retina we will not be able to see
anything so now here we introduce a term
watt power of a combination so power of
accomodation is the ability of the eye
lens to adjust its focal length to see
both distant and close objects now as we
said that the lens and become fat the
lens can become thin but there is a
limitation to that also now there has to
be a certain limit up to which it can
become thin similarly there has to be a
certain limit up to which it can become
thick so that ability or that
flexibility of the islands is what we
call power of accomodation that means
how much the lens can accommodate how
much the lens can adjust to ensure that
the image is formed on the retina so as
we saw that these are like the two
extreme conditions where the thickness
of the lens changes now the closest
distance of an object for which the lens
can focus the light on the retina that
is known as the least distance of
distinct vision now if you have ever
observed it for yourself that if you
take a book and bring it extremely close
to your eyes will you be able to
the book you can't if you haven't read
it here try it now bring the book
extremely close to your eyes almost
touching your eyes you don't be able to
read the book No so when the book is so
near to you that time also you can't
read it because now the distance of the
object has reduced so much that the lens
is not able to you know adjust its focal
length so much to produce an image of
the retina so the image is not being
formed on the retina so there is a
minimum distance minimum distance of the
object for which their lens can focus
the image on retina so that distance is
called least distance of distinct vision
that means that is the minimum distance
at which you can very distinctly see
that object and this distance is also
known as the near point that point where
the object should be located that point
is termed as the near point and for a
normal eye that near point is 25
centimeters so if you place any object
if you place a book at a distance of 25
centimeters from your eye you will be
able to read it very comfortably but if
you bring it maybe some to a distance of
10 centimeters from your eyes you will
not be able to read it clearly
however this value of near point often
increases with age because as a person
ages the ability of the lens or the
power of accommodation of the lens
reduces the lenses no more that flexible
as a result you would have seen that
elderly people often bring a book you
know they really need to see it very
closely to be did otherwise they they do
not get to read it very properly so this
the value tend to increase at with age
so for a normal eye the near point is 25
centimeters at the far point is infinity
that means the fire point can be
anywhere because we already saw in the
ray diagram that if the object is far
away even if the object is at infinity
the lens can adjust itself in such a way
that the image is formed on the
principle focus and the fluid
focus lies on the retina so fire point
could be infinity but the near point has
to be 25 centimeters so with this
figured an idea that about how our eyes
reduce images of objects and then how
our brain interprets those images so
that we can see the objects as they are
thank you please visit exam fee or comm
for free quality education you can learn
with a simple four-step learning process
wherein you can watch video lessons you
can ask your questions you can refer
notes and you can take a free online
test we have content for class 6 to 12
on physics chemistry mathematics and
biology along with practical videos so
please subscribe to our channel for
daily updates thank you
About this Video
4.9/5 Rating
Apr 20, 2026 Last updated
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