Compound microscope in urdu hindi, 10th class physics wallah sabaq chapter 12 by atif ahmed.
Queries solved in this video
1. What is microscope
2. What is compound microscope
3. How to make ray disgram of compound microscope
4. Magnification
5. How image form in compound microscope
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telescope to view distant stars.
12.13 COMPOUND MICROSCOPE
Compound microscope has two converging lenses, the
objective and the eyepiece and is used to investigate
structure of small objects


It gives greater magnification than a single lens.

The objective lens has a short focal length, ƒ cm. o

The eyepiece has a focal length, ƒ of a few cm. e
Magnification of the Compound Microscope
Magnification can be determined through the ray diagram as
shown in Fig. 12.32. Objective forms a small image inside
I1
the focal point of eyepiece. This image acts as an object for
the eyepiece and the final larger image I is formed outside 2
the focal point of the objective.
Fig. 12.32: Ray diagram for compound microscope
The magnification of a compound microscope is given by
where L is the length of a compound microscope which is
equal to the distance between objective and eye piece, d is
distance of final image from eye, f
and f are the focal lengths
o e
of objective and eye piece respectively.
Uses of Compound Microscope
A compound microscope is used to study bacteria and other
micro objects. It is also used for research in several fields of
sciences like, Microbiology, Botany, Geology, and Genetics.

12.12 SIMPLE MICROSCOPE
A magnifying glass is a convex lens which is used to produce
magnified images of small objects. Hence, it is also called
simple microscope. The object is placed nearer to the lens
than the principal focus such that an upright, virtual and
magnified image is seen clearly at 25cm from the normal eye.
Magnifying Power
Let be the angle subtended at the eye by a small object
when it is placed at near point of the eye(Fig.12.30-a).
If the object is now moved nearer to the eye(Fig.12.30-b), the
angle on the eye will increase and becomes , but the eye will
not be able to see it clearly. In order to see the object clearly

This is also called Snell's law.
.

o
The angle of incidence for which the angle of refraction becomes 90 is called critical
angle. When the angle of incidence becomes larger than the critical angle, no
refraction occurs. The entire light is reflected back into the denser medium. This is
known as total internal reflection of light.

A simple microscope, also known as a magnifying glass, is a convex lens which is
used to produce magnified images of small objects.

A compound microscope is used to investigate structure of small objects and has
two converging lens, the objective and the eyepiece.

Telescope is an optical instrument which is used to observe distant objects using
lenses or mirrors. A telescope that uses two converging lenses is called refracting
telescope. A telescope in which the objective lens is replaced by a concave mirror is
called reflecting power telescope.

The magnifying power is defined as “the ratio of the angle subtended by the image as
seen through the optical device to that subtended by the object at the unaided eye”.

The resolving power of an instrument is its ability to distinguish between two closely
placed objects.

The ability of the eye to change the focal length of its lens so as to form a clear image
of an object on its retina is called its power of accommodation.

The disability of the eye to form distinct images of distant objects on its retina is
known as nearsightedness. The nearsighted eye can be corrected with glass or
contact lenses that use diverging lenses Light rays from the distant objects will
.
diverge by this lens before entering the eye.

The disability of the eye to form distinct images of nearby objects on its retina is
known as farsightedness. This defects can be corrected with the aid of a suitable
converging lens. The lens refracts the light rays more towards the principal axis
before they enter the eye.
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