This document provides an overview of concepts related to microscopes, telescopes, and their resolving power. It defines key terms like least distance of distinct vision, visual angle, and magnifying power. It then explains the principles of simple microscopes, compound microscopes, and telescopes under stressed and relaxed vision. The document also discusses how resolving power depends on factors like wavelength and aperture diameter. Finally, it includes several practice problems related to calculating magnifying powers and resolving distances for different optical instruments.

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5. We’ll do in depth study of
● Some Important concepts
● Simple microscope
● Compound microscope
● Astronomical telescope
● Resolving power - Microscope & telescope

6. Some important terms
LDDV
Minimum distance for the clear vision
of an object. This distance is called
least distance of distinct vision (+D).
For normal eye this distance is 25 cm.

7. Some important terms
Visual angle
The size of an object as sensed by us is related
to the size of the image formed on the retina.
Optical instruments are used to increase this
angle artificially in order to improve the clarity.

8. Some important terms
Magnifying power
Magnifying power is the factor by
which the image on the retina
can be enlarged by using the
microscope or telescope.
For microscope,
M =
visual angle formed by
final image
visual angle formed by
object if it was kept at D
Remember this is
angular magnification,
not linear magnification

10. Simple microscope
Stressed vision
(When the image is formed at LDDV)

11. Simple microscope
Stressed vision
(When the image is formed at LDDV)

12. Simple microscope
Relaxed vision
(When the image is formed at infinity)

13. Simple microscope
Relaxed vision
(When the image is formed at infinity)

15. Compound microscope
Stressed vision
(When the image is formed at LDDV)

16. Compound microscope
Relaxed vision
fe=
ue
E
h
B
B’
h’
fo
u
O
(When the image is formed at infinity)

18. Telescope
Stressed vision fo
fe
E
B’
h
u
O
α
α
β
A’
x

19. Telescope
Stressed vision fo
fe
E
B’
h
u
O
α
α
β
A’
x
m = β/α
= h/x /
h/fo
m = fo/x

20. Telescope
Relaxed vision

21. Telescope
Relaxed vision

22. Resolving power

23. 𝜃
Objective
Δd
Resolving power (Microscope)
The resolving power of a microscope is defined as
the reciprocal of the distance between two
objects which can be just resolved when seen
through the microscope.
Resolving power depends on
● wavelength λ
● refractive index of the medium between the
object and the objective
● half angle of the cone of light from one of the
objects β.

24. Resolving power (Telescope)
The resolving power of a telescope is defined as
the reciprocal of the smallest angular separation
between two distant objects whose images are
seen separately.
Resolving power depends on
● wavelength λ
● diameter of the objective a.
RP d𝜃
Objective

26. The separation between two microscope particles is measured PA and
PB by two different lights of wavelength 2000 Å and 3000 Å respectively,
then
A
B
C
D
PA > PB
PA < PB
PA < 3/2 PB
PA = PB

27. The separation between two microscope particles is measured PA and
PB by two different lights of wavelength 2000 Å and 3000 Å respectively,
then
A
B
C
D
PA > PB
PA < PB
PA < 3/2 PB
PA = PB

28. A telescope of aperture diameter 5.5 m is used to observe the moon
from the earth. Distance between the moon and earth is 4 x 105 km. The
minimum distance between two points on the moon’s surface which can
be resolved using this telescope is close to (Wavelength of light is
5500 Å)
A
B
C
D
60m
50m
500m
50m

29. A telescope of aperture diameter 5.5 m is used to observe the moon
from the earth. Distance between the moon and earth is 4 x 105 km. The
minimum distance between two points on the moon’s surface which can
be resolved using this telescope is close to (Wavelength of light is
5500 Å)
A
B
C
D
60m
50m
500m
50m

30. In a compound microscope the focal length of objective lens is 1.2 cm
and focal length of eyepiece is 3.0 cm. When object is kept at 1.25 cm in
front of objective, final image is formed at infinity. Magnifying power of
the compound microscope should be ? [JEE Mains
(April 2014) ]
A
B
C
D
200
100
400
150

31. In a compound microscope the focal length of objective lens is 1.2 cm
and focal length of eyepiece is 3.0 cm. When object is kept at 1.25 cm in
front of objective, final image is formed at infinity. Magnifying power of
the compound microscope should be ? [JEE Mains
(April 2014) ]
A
B
C
D
200
100
400
150

32. Find the magnifying power of a compound microscope whose objective
and eyepiece are of focal lengths 4.0 cm and 6.0 cm respectively and
the object is placed 5.0 cm beyond the objective. Assume that the final
image is formed at the least distance of distinct vision (25 cm).
A
B
C
D
-20.7
-30.2
-20.0
+27.0

33. Find the magnifying power of a compound microscope whose objective
and eyepiece are of focal lengths 4.0 cm and 6.0 cm respectively and
the object is placed 5.0 cm beyond the objective. Assume that the final
image is formed at the least distance of distinct vision (25 cm).
A
B
C
D
-20.7
-30.2
-20.0
+27.0

34. The focal length of objective of an astronomical telescope is 1 m. If the
magnifying power of telescope is 20, then what is length of telescope
for relaxed eye?
A
B
C
D
85 cm
95 cm
105 cm
115 cm

35. The focal length of objective of an astronomical telescope is 1 m. If the
magnifying power of telescope is 20, then what is length of telescope
for relaxed eye?
A
B
C
D
85 cm
95 cm
105 cm
115 cm

36. A
B
C
D
+5
+10
+14
+20
A wire mesh consists of squares each of side 1 mm. It is placed at distance of
9.0 cm from a magnifying glass of focal length 10 cm. It is viewed by placing the
eye close to the lens. what is the magnification produced by the lens?

37. A wire mesh consists of squares each of side 1 mm. It is placed at distance of
9.0 cm from a magnifying glass of focal length 10 cm. It is viewed by placing the
eye close to the lens. what is the magnification produced by the lens?
A
B
C
D
+5
+10
+14
+20

38. A wire mesh consists of squares each of side 1 mm. It is placed at a
distance of 9.0 cm from a magnifying glass of focal length 10 cm. It is
viewed by placing the eye close to the lens. What is the area of each
square in the virtual image of the mesh? (take the result from last
question about magnification)
A
B
C
D
50 mm2
500 mm2
1000 mm2
100 mm2

39. A wire mesh consists of squares each of side 1 mm. It is placed at a
distance of 9.0 cm from a magnifying glass of focal length 10 cm. It is
viewed by placing the eye close to the lens. What is the area of each
square in the virtual image of the mesh? (take the result from last
question about magnification)
A
B
C
D
50 mm2
500 mm2
1000 mm2
100 mm2

40. A refracting (astronomical) telescope, when in normal adjustment, has a
magnifying power of 6 and the objective and the eyepiece are 14 cm
apart. Find the focal lengths of the lenses of the telescope.
A
B
C
D
fe= 2 cm, fo= 12 cm
fe= 12 cm, fo= 12 cm
fe= 12 cm, fo= 2 cm
fe= 5 cm, fo= 12 cm

41. A refracting (astronomical) telescope, when in normal adjustment, has a
magnifying power of 6 and the objective and the eyepiece are 14 cm
apart. Find the focal lengths of the lenses of the telescope.
A
B
C
D
fe= 2 cm, fo= 12 cm
fe= 12 cm, fo= 12 cm
fe= 12 cm, fo= 2 cm
fe= 5 cm, fo= 12 cm

42. A telescope has an objective of focal length 120 cm and an eyepiece of
focal length 5.0 cm. Find the magnifying power of the telescope when it
is used to view distant objects when (a) the telescope is in normal
adjustment, and (b) the final image is formed at the least distance of
distinct vision (25 cm)
A
B
C
D
(a) 20, (b) 40
(a) 33.5, (b) 40
(a) 20, (b) 24.8
(a) 24, (b) 28.8

43. A telescope has an objective of focal length 120 cm and an eyepiece of
focal length 5.0 cm. Find the magnifying power of the telescope when it
is used to view distant objects when (a) the telescope is in normal
adjustment, and (b) the final image is formed at the least distance of
distinct vision (25 cm)
A
B
C
D
(a) 20, (b) 40
(a) 33.5, (b) 40
(a) 20, (b) 24.8
(a) 24, (b) 28.8

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