Page 57 - Physics 10_Float

GEOMETRICAL OPTICS

 It gives greater magnification than a single lens.
 The objective lens has a short focal length, ƒ < 1 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 I 1
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.
L Compound microscops
Eyepiece Objective lens has smaller
Objective focal length, than the
Object eyepiece.
P Eye Distance between the
Fo F e Q F e
objective lens and the
T O F
o I 1 eyepiece is greater than f +f .It
0 e
R is used to see very small
I f
2 o objects.
Final
image
S f e
d
Fig. 12.32: Ray diagram for compound microscope

The magnification of a compound microscope is given by
L d
M = (1 + )
f f
o e
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 Astronomical telescope
of objective and eye piece respectively. Objective lens has larger focal
length than the eyepiece.
Uses of Compound Microscope Distance between the
A compound microscope is used to study bacteria and other objective lens and the
micro objects. It is also used for research in several fields of eyepiece is equal to f +f .
0
e
It is used to see distant
sciences like, Microbiology, Botany, Geology, and Genetics.
astronomical objects.
12.14 TELESCOPE
Telescope is an optical instrument which is used to observe
distant objects using lenses or mirrors. A telescope that uses

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