L9 : Spherical Mirror - Light, Science, Class 7 Video Lecture

hello friends this video on light park 9
is brought to you by example calm no
more fear from exam so now we are going
to learn about something even more
interesting have you ever observed the
real back view middle of the car so when
you look at the back view middle of the
time you are able to get a view of your
back side right so with a Brita which is
such small in size in that mirror you
are able to see the complete entire
image of a car a car is such big in size
but still live inside such a small
mirrors you are able to see the image of
such a big car how is it possible that
is possible only when a diminished image
is being formed only then an image which
is smaller in size that the object is
then formed only in that case we will be
able to see the image of that object
right so there exists different types of
mirrors where the size of the image is
either smaller than the object or larger
than the object and because of this
beautiful property of such litters they
find a variety of applications where
they are used even if you have ever
visited a dentist's place you will see
that they have a glass with which they
observe your they do examination of your
teeth so if you say that ok something
has happened in my gum so they make use
of that glass to see your gums that
because with this glass or with this
mirror they are able to see a magnified
or a bigger image of the same tooth
which helps them easy to diagnose it
more easily so that means you have a
couple of applications of these kind of
mirrors and these kind of mirrors which
produce images which are either smaller
in size or larger in size than the
object they all fall in the category of
spherical mirrors so till now we were
talking about clean mirrors where the
reflective surface was a plain surface
but now we will talk about mirrors where
the reflective surface is not a clean
circle
instead it is a curved surface so these
two examples which I have used in the
screen whether you talk about the
rearview mirror of the car or you talk
about the dentist may die in both these
cases I am sure you would understand
that clean mirrors will not solve the
purpose because the plane mirrors the
image that is formed that is of the same
size as that of the object so in case of
the rearview mirror if the same size
image is gone you will not be able to
see the entire background scenery as you
can see here similarly if the dentist is
not able to get an enlarged image of the
tooth then there is no point using that
mirror because the correct size in the
tooth is anyways visible to the dentist
with his naked eye so then what is the
point of having this special mirror so
let us see what is a spherical mirror so
how do we define the spherical mirror
how do we get a statical mirror the word
spherical mirror defines itself
spherical something which is derived
from a sphere so basically you look at
this mirror it is in the form of a big
sphere right of which only a part is
being visible on this picture
so basically spherical mirror is nothing
but a part of a reflective spherical
surface so it is something like of you
imagine a big sphere a big ball which is
completely reflective which is like a
mirror which is not a plane mirror
instead of mirror which is in the shape
of a sphere so if you cut a part of this
sphere what you get is a spherical
mirror so if you look at these mirrors
these are spherical mirrors you see this
is like cut from a sphere only this part
similarly when you look at this mirror
this is also like a part of a big sphere
right so these are all examples of
spherical mirror so we call it a part of
a big sphere where the entire sphere is
a reflective circuit surface so if you
cut any part of the sphere
what you will see you will get an inner
surface of the sphere you will get an
outer surface of the sphere right so
this is how it would be now in those
mirrors where the outer surface is those
mirrors in which the outers have faces
not reflective that is concave mirror as
you can see here this is the reflective
surface so this is the shiny surface so
wherever you have these hairlike
structures that is the non shiny surface
so basically whenever the inner surface
is shiny that kind of mirror is called a
concave mirror so it is something like
this that inner surface let's say this
is the outer surface so the inner
surface wherever the inner surface is
shiny that is concave cave means
something which goes inside right and
the outer surface if the outer surface
is shiny then it is called a convex
mirror so here in this case you see the
outer surface is shiny this surface is
shiny so this is a convex mirror in this
case the inner surface is shiny so this
is a concave mirror so that's how we
differentiate the two types of mirror
the most common example of spherical
mirrors you can think of is a spoon so
how does a spoon look like so this is
how a spoon looks like right so you have
an outer surface you have an inner
circle so you actually have both concave
and convex mirrors in a spoon so that's
how the you know like that's how the
spherical mirrors are that that's the
best example that you can think of when
it comes to selling mirrors so let us
perform certain experiments to see how
images are formed with spherical mirrors
so you see a couple of pictures have
been shown we're using the same spoon so
this you see this is the back side of
the spoon so back side is the outer
surface that is the back side of the
spoon acts as a convex mirror so you see
the image that is formed is erect
straight image is being formed now when
you look at the
say the inner surface of the spoon so
that is the concave mirror so in this
you see an inverted image response you
see the head part is at the bottom so an
inverted image is being formed so this
itself shows that the two sides of the
spoon gives us different types of images
that's because the two sides of the
spoon are two different types of mirrors
again when you bring an object very
close to the concave surface of the
spoon that is the front surface of the
spoon you see that the images are like
erect so here also it was the front
surface so both of these I like the
concave surface of the spoon but in this
case the image was inverted in this case
the image is in it so what is the
difference in this case the object is
located quite far from the middle so you
look at the distance of the object from
the mirror it is quite fine but in this
case the object is located very close to
the mirror so that's why it is giving an
erect image so basically in a concave
mirror the type of image that will be
formed that will vary with the distance
of the image from the mirror so we will
learn more about the image formation
with both concave and convex mirrors so
what I am trying to show you is with
different types of spherical mirrors you
get different types of images even with
the same type of spherical mirror you
get different types of images based on
the location or the distance of the
object from the mirror so there are a
lot of factors which decide which type
of image will be formed with a mirror
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