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Physics Part-II

Ray Optics and Optical Instruments

A compound microscope consists of an objective lens of focal l

Physics Part-II

Class 12

NCERT

Chapter 1: Ray Optics and Optical Instruments

41 questions

What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

A compound microscope consists of an objective lens of focal length

2.0 c m

and an eyepiece of focal length

6.25 c m

separated by a distance of

15 c m

. How far from the objective should an object be placed in order to obtain the final image at:
(a) the least distance of distinct vision

(25 c m)

, and
(b) at infinity? What is the magnifying power of the microscope in each case?

A person with a normal near point (25 cm) using a compound microscope with objective of focal length 8.0 mm and an eyepiece of focal length 2.5 cm can bring an object placed at 9.0 mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope.

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Question

Medium

Solving time: 5 mins

A compound microscope consists of an objective lens of focal length $2.0 c m$ and an eyepiece of focal length $6.25 c m$ separated by a distance of $15 c m$ . How far from the objective should an object be placed in order to obtain the final image at:
(a) the least distance of distinct vision $(25 c m)$ , and
(b) at infinity? What is the magnifying power of the microscope in each case?

Views: 5,934 students

Updated on: Feb 29, 2024

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Physics Part-II (NCERT)

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Benjamin Discussed

A compound microscope consists of an objective lens of focal length

2.0 c m

and an eyepiece of focal length

6.25 c m

separated by a distance of

15 c m

. How far from the objective should an object be placed in order to obtain the final image at:
(a) the least distance of distinct vision

(25 c m)

, and
(b) at infinity? What is the magnifying power of the microscope in each case?

11 mins ago

Discuss this question LIVE

11 mins ago

Text solutionVerified

Focal length of the objective lens

f_{1} = 2 c m

Focal length of the eyepiece,

f_{2} = 6.25 c m

Distance between the objective lens and the eyepiece,

d = 15 c m

Least distance of distinct vision,

d^{'} = 25 c m

Image distance for the eyepiece,

v_{2} = - 25 c m

bject distance for the eyepiece =

u_{2}

According to the lens formula

\frac{1}{f _{2}} = \frac{1}{v _{2}} - \frac{1}{u _{2}}

\frac{1}{6.25} = \frac{1}{- 25} - \frac{1}{u _{2}}

u_{2} = - 5 c m

Image distance for the objective lens

v_{1} = d + u_{2} = 15 - 5 = 10 c m

According to the lens formula

\frac{1}{f _{1}} = \frac{1}{v _{1}} - \frac{1}{u _{1}}

\frac{1}{2} = \frac{1}{10} - \frac{1}{u _{1}}

u_{2} = - 2.5 c m

The magnifying power of a compound microscope is given by the relation

m = \frac{v _{1}}{∣ u _{1} ∣} (1 + \frac{d ^{'}}{f _{2}})

m = \frac{10}{2.5} (1 + \frac{25}{6.25}) = 20

b)The final image is formed at infinity

Image distance for the eyepiece

v_{2} = \infty

According to the lens formula

\frac{1}{f _{2}} = \frac{1}{v _{2}} - \frac{1}{u _{2}}

According to the lens formula

\frac{1}{6.25} = \frac{1}{\infty} - \frac{1}{u _{2}}

u_{2} = - 6.25 c m

Image distance for the objective lens

v_{1} = d + u_{2} = 10 - 6.25 = 8.75

Object distance for the objective len =

u_{2}

According to the lens formula

\frac{1}{f _{1}} = \frac{1}{v _{1}} - \frac{1}{u _{1}}

\frac{1}{2} = \frac{1}{8.75} - \frac{1}{u _{1}}

u_{2} = - 2.59 c m

The magnifying power of a compound microscope is given by the relation:

\frac{v _{1}}{∣ u _{1} ∣} (\frac{d ^{'}}{∣ u _{2} ∣}) = 13.51

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Practice more questions from Physics Part-II (NCERT)

What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.

A compound microscope consists of an objective lens of focal length

2.0 c m

and an eyepiece of focal length

6.25 c m

separated by a distance of

15 c m

. How far from the objective should an object be placed in order to obtain the final image at:
(a) the least distance of distinct vision

(25 c m)

, and
(b) at infinity? What is the magnifying power of the microscope in each case?

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Question Text	A compound microscope consists of an objective lens of focal length $2.0 c m$ and an eyepiece of focal length $6.25 c m$ separated by a distance of $15 c m$ . How far from the objective should an object be placed in order to obtain the final image at: (a) the least distance of distinct vision $(25 c m)$ , and (b) at infinity? What is the magnifying power of the microscope in each case?
Updated On	Feb 29, 2024
Topic	Ray Optics and Optical Instruments
Subject	Physics
Class	Class 12
Answer Type	Text solution:1 Video solution: 3
Upvotes	345
Avg. Video Duration	2 min

Text solutionVerified

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