Exam Master CHSE ODISHA ~ Physics)

Q.7 With a simple microscope, if the final
image is located at infinity, then its magnifying power is

(a) DIA (b) 1+ DIf (c) ID (d) Dxf D Sol (a) When final image at infinity, M =

Q.8 An observer looks at a tree of height 15 m with a telescope of magnifying power 10. To him the tree appears [Textbook] (a) 10 times taller (b) 15 times taller (c) 10 times nearer

Sol (c) Since, magnifying power is 10. So, tree appears 10 times nearer. (1)

(d) 15 times nearer

Q.9 An astronomical telescope has a converging eyepiece of focal length 5 cm and objective of focal length 80 cm. When the final image is formed at the least distance of distinct vision (25 cm), the separation between the two lenses is [Textbook] (a) 75 cm (b) 80 cm (c) 84.2 cm (d) 85 cm

Sol (c) :: Separation between the

two lenses, D fe 25 x 5 L = f. + = 80+ - 84.2 cm fe+D 25 + 5

(a) 5D Q.10 For an astronomical telescope used in normal adjustment, objective and the eyepiece are separated by a distance of 55 cm. If the magnifying power of the telescope is 10, the power of the objective is [Textbook] (b) 50D (c) 2D (d) 0.5D

Sol (c) Since, for normal adjustment,

[Textbook]

M =

and L = f. + fe

fe 10 = fo and 55 cm = f. + fe fe =

which give f. = 50 cm and fe = 5 cm. =

1 Hence, power, P. f. =

f.

50 x 10-2

P. = 2D

Q.11 In a compound microscope, the focal lengths of objective and eyepiece are 1.2 cm and 3 cm, respectively. If the object is put 1.25 cm away from the objective lens and the final image is formed at infinity, the magnifying power of the microscope is [Textbook]

(a) 150 (b) 200 (c) 250 (d) 400

[Textbo, Q.12 In order to increase the magnifying power of a microscope,

(a) the focal powers of the objectives and eyepiece should

(1)

(b) objective should have small focal length and the eyepiece large

1

large

(c) Both should have large focal lengths (d) the objectives should have large focal length and small focal length

eyepiece should have

Sol (6) For high magnifying power of microscope, the objective should have small focal length and the eyepiece should have large focal length.

Q.13 You are supplied with four convex lenses of focs lengths 100 cm, 25 cm, 3 cm and 2 cm. For designing an astronomical telescope, you will us lenses of focal lengths [Textbook (a) 100 cm and 25 cm (b) 100 cm and 3 cm (c) 25 cm and 2 cm (d) 100 cm and 2 cm

Sol (d) We use objective of largest focal length, i.e. 100c and eyepiece of smallest focal length, i.e. 2 cm. 11

Q.14 The length of a simple astronomical telescope is

(1)

(a) the difference of the focal lengths of two (b) half the sum of the focal lengths (c) the sum of the focal lengths (d) product of the focal lengths

(a) f.xfe (b) filfe (c) fo+fe (d) felt.

Sol (c) Length of a simple astronomical telescope, L = f. + fe

Q.15 A compound microscope has an objective and eyepiece as thin lenses of focal lengths 1 cm and 5 cm, respectively. The distance between the objective and eyepiece is 20 cm. The distance at which the object must be placed in front of the objective, if the final image is located at 25 cm from the eyepiece is numerically. [Textbooks (a) 95/6 cm (b) 5 cm (c) 95/89 cm Sol (c) Given, f. = 1 cm, fe = 5 cm (d) 25/6 cm

and

Sol (6) As,

1 1 1 v fo u. =

(1)

Or

[Textbook The length of an astronomical telescope tube for normal vision is

L = 20 cm.

1.2 x 1.25 Vo =

f

D fe L = v. + D+ fe

and

1 u. f. u 1 =

0.05

1.2 x 1.25 x 25 So, V. D M = 1.25% 0.053

= M = 200 uo fe

25 x 5 V = 20 -

30 1 1 1

95 u. = cm

cm 6 6 89

89

95

95

3

95

(1)

î

[Textbook lenses

(1

(216