A microscope isS used to incregse the visual angle of the images of the objects O

very small size. The magnifying power can be increased by using two lenses.

Construction:

A compound microscope consists of a tube with a lens at each end. It comprises

two convex lenses

Obiective Lens:

It is a convex lens which is nearer to the object. It has short focal length (< lemn)

Evepiece or Occular Lens:-53

It is conVex lens placed before the eye, It has relatively long focal length Frame

The microscope contains a frame that holds objective and eye-piece lenses with

'stage' to place the object. There is a concave mirror to gather light and its also contain

Some adjusting Screws.

WORKING:

A small object is placed just beyond the focus of the objective. The objective len

forms a real, inverted and magnified image (A B).

The eye-piece is used as a magnitying glass to see the image formed by t

objective. The final image (A B) seen by the eye through the microscope is inverte

Victorl10 Chagter-10

COLLEGE PHYSIC5

Assumptions:

Firat feor

() All ryas are paraxial.

(2) The eyes is close to the eye-piece lens

(3)

The microscope 1s in normal adjustment.

Magnilving Power:

When the microscope is in normal adjustment, the final image is at the near point

Let magnifying power of the compound microscope= M

Let linear magnification of the objective=M

Let angluar magnification of the eye-piece=M2

Let focal length of the objective=f

Let focal length of the eye-piece = f2

The magnification of a microscope is the product of the magnification of its

objective lens and eyepiece lens

Magnifying power of compound microscope is: M = MiX M2. )

Linear magnification of the objective is

ALTERNATIVE FORMULA

size of image

size of object

distance of image from objective

distance of objectfromobectiveMagnification of the objective,

ABM=AR= -(1)Mi ABP

Magnification of the eye picce,

AB92 2

M-AB P2

Thus Mi

Since

Pif and qi L (length of

Magnification of the mieroscope,

microscpe), we have

The eye-piece acts as a magnifying glass.

ence angular magnification of the 

Where d" is the least distance of distinct

vision (25cm for )