A lens
is made from a transparent material (glass/plastic).
Lens is a piece
of transparent material which has one or both sides spherical.
A lens which is
thick at the middle and thinner at the edges is
called convex lens.
When parallel
light rays strike the surface of a convex lens these rays converge at a
point called focal point (F). So it is called converging
lens.
The lens, which
is thin at the middle and thicker at the edges is
called concave lens.
When parallel
light ray stick the surface of concave lens then these rays are diverged
after passing through lens. When these refracted rays are retracted backward,
these seem to meeting at focal point. As these lens diverges the rays, so it is
called diverging lens.
The center
O of the lens is known as the optical center of the lens.
The center of
the sphere of which any surface of the lens is a part is known as its center of
curvature.
A straight line
joining the center of curvatures is called the principle axis.
Parallel rays
after refraction through a convex lens converge at a point F which is called
the principal focus of the lens.
The distance
between the optical center and the principal focus is known as focal
length of the lens.
The image that
can be obtained on the screen is known as real image.
Real image of an object
can be obtained on the screen by a convex lens.
Virtual image of an object
can be obtained on screen by concave lens.
A camera
is used to obtain image on the sensitive film. It works like human eye.
Lenses are used in
microscope, telescope, cameras, and projectors etc.
A person
suffering from short sightedness cannot see far off objects clearly. concave
lenses
A person
suffering from long sightedness cannot see the near objects clearly convex
lenses.
There are
various forms of convex and concave lenses.
A camera is an optical
instrument.
The lens of
camera forms a real, small and inverted image
of an object.
Double convex
lens: when both the surfaces of a convex lens are curved outward then it
is called double convex lens or Bi-convex lens.
Plano convex
lens: if one of the surfaces of a lens is convex and other is plane,
then it is called a Plano convex lens.
Double concave
lens: when both the surfaces of a lens are concave or curved inward then
it is called double concave lens or Bi-concave lens.
Plano concave
lens: if one of the surfaces of a lens is concave and other is plane
then it is called a Plano-concave lens.
Concave- convex
lens: if one of the surface of a lens is convex and the other is concave
such that the central region of the lens is thicker than edges then it is
called a concave-convex lens.
A lens which is thick at the middle
and thinner at the edges is called………
a) convex lens
b) concave lens
c) both a an b
d) none of these
A lens which is thin at the middle
and thicker at the edges is called……NTS PST15/12/2019 (8:30)
a) convex lens
b) concave lens
c) both a an b
d) none of these
