L14 : Image formation by Concave & Convex Lens - Light, Science, Class 7 Video Lecture

hello friends this video on light part
14 is brought to you by example calm no
more pure from exam so let us now talk
about image formation by convex lenss
the way we discussed about mirrors now
we are going to discuss about the lens
now remember one thing that the image
formed by the lens can be seen from the
side opposite to that of the object so
when you have the object here so this is
the lens and then you get to see the
image here so you actually need to see
through the lens in order to view the
image so in case of a convex lens you
see the image formation is going to be
similar to that of concave mirror so you
see as you bring the object nearer to
the mirror what happens the size of the
image keeps increasing however the image
is still important now when you bring
the object more near to the middle you
see the image becomes all the more
enlarged and finally when the object is
very close to the mirror you actually
get to see a highly enlarged image but
in this case it is also erect
so you see this is where the object is
and then you have the mirror and you
have to be on the other side of the
mirror you know I am sorry
lens you have to be on the other side of
the lens to view the image so I hope it
is clear from where you have to see this
is your object in front of the object is
the lens and then on the lens itself you
can see the image like this so this
shows that in case of convex lens the
images formed can be of a variety of
types like you can have diminished
inverted image you can also have image
of the same size and inverted you can
also have enlarged image you can even
have a large erect image so you have the
possibility of having both real images
as well as virtual images so both
options are open a variety of image
types are formed with a convex lens so
when you look at the review for image
formation by convex lens you see that it
is almost similar to that of mirror
now there are a few differences in terms
of the terminologies like in case of
mirror we just talked about one
principal focus then is just one focus
but in case of lens there are two focus
that is F 1 and F think that's because
here you have a lens is nothing but a
combination of two mirrors so this
surface will have one focus this surface
will have another focus somewhere here
so that is why they have been named as F
1 and F 2 so please do not get confused
with that and variable we have used 2 F
1 that is nothing but the center of
curvature C 1 or similarly whenever ever
you have two F 2 that is nothing but C
towards the center of curvature of the
second surface so that's how looking at
this I think this should be pretty much
clear to you by now so let us quickly
look at the image formation by a concave
lens so in a concave lens we always find
your direct images diminished images and
now these are virtual images and that
that's why we get to see them on the
other side of the lens so that's one
speciality of the concave lens so that
means concave lens behavior-wise is very
much similar to that of the convex
mirror so again a quick review on image
formation so when you look at the review
of image formation by concave lens so
every time just like a convex mirror you
see that diminished image virtual images
are formed it is just that it occupies
very far away so the image will be all
the more diminished but anyways wherever
the object is located image will always
be smaller in size than the object so
now let us look at some of the
interesting things now if I give you
this example of a magnifying glass what
do you think which lens is this so now
can you answer this question so looking
at this image what do you think what
kind of image is form an enlarged image
is formula right so do you think
you will ever be able to get an enlarged
image with a concave lens
no because concave lens always produces
diminished image so obviously this is
nothing but a convex lens so because we
know that convex lens because on Kiev
lens produces diminished images but
convex lens produces enlarged images so
this is a convex lens so see this is how
you have to judge that which type of
lens is used in a particular purpose
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