#### Chapters

Chapter 2: Physics and Mathematics

Chapter 3: Rest and Motion: Kinematics

Chapter 4: The Forces

Chapter 5: Newton's Laws of Motion

Chapter 6: Friction

Chapter 7: Circular Motion

Chapter 8: Work and Energy

Chapter 9: Centre of Mass, Linear Momentum, Collision

Chapter 10: Rotational Mechanics

Chapter 11: Gravitation

Chapter 12: Simple Harmonics Motion

Chapter 13: Fluid Mechanics

Chapter 14: Some Mechanical Properties of Matter

Chapter 15: Wave Motion and Waves on a String

Chapter 16: Sound Waves

Chapter 17: Light Waves

Chapter 18: Geometrical Optics

Chapter 19: Optical Instruments

Chapter 20: Dispersion and Spectra

Chapter 21: Speed of Light

Chapter 22: Photometry

#### H.C. Verma Concept of Physics Part-1 (2018-2019 Session) by H.C Verma

## Chapter 19: Optical Instruments

#### Chapter 19: Optical Instruments Exercise MCQ solutions [Page 430]

Can virtual image be formed on the retina in a seeing process?

Can the image formed by a simple microscope be projected on a screen without using any additional lens or mirror?

The angular magnification of a system is less than one. Does it mean that the image formed is inverted?

A simple microscope using a single lens often shows coloured image of a white source. Why?

A magnifying glass is a converging lens placed close to the eye. A farsighted person uses spectacles having converging lenses. Compare the functions of a converging lens used as a magnifying glass and as spectacles.

A person is viewing an extended object. If a converging lens is placed in front of his eyes, will he feel that the size has increased?

The magnifying power of a converging lens used as a simple microscope is `(1+D/f).` A compound microscope is a combination of two such converging lenses. Why don't we have magnifying power `(1+D/f_0)(1+D/f_0)`?In other words, why can the objective not be treated as a simple microscope but the eyepiece can?

By mistake, an eye surgeon puts a concave lens in place of the lens in the eye after a cataract operation. Will the patient be able to see clearly any object placed at any distance?

The magnifying power of a simple microscope is given by `1+D/f` , where *D* is the least distance for clear vision. For farsighted persons, *D* is greater than the usual. Does it mean that the magnifying power of a simple microscope is greater for a farsighted person as compared to a normal person? Does it mean that a farsighted person can see an insect more clearly under a microscope than a normal person?

Why are the magnification properties of microscopes and telescopes defined in terms of the ratio of angles and not in terms of the ratio of sizes of objects and images?

An object is placed at a distance of 30 cm from a converging lens of focal length 15 cm. A normal eye (near point 25 cm, far point infinity) is placed close to the lens on the other side. (a) Can the eye see the object clearly? (b) What should be the minimum separation between the lens and the eye so that the eye can clearly see the object? (c) Can a diverging lens, placed in contact with the converging lens, help in seeing the object clearly when the eye is close to the lens?

A compound microscope forms an inverted image of an object. In which of the following cases it it likely to create difficulties?

Looking at small germs.

Looking at circular spots.

Looking at a vertical tube containing some water.

#### Chapter 19: Optical Instruments Exercise MCQ solutions [Page 431]

The size of an object as perceived by an eye depends primarily on

actual size of the object

distance of the object from the eye

aperture of the pupil

size of the image formed on the retina.

The muscles of a normal eye are least strained when the eye is focussed on an object

far away from the eye

very close to the eye

at about 25 cm from the eye

at about 1 m from the eye

A normal eye is not able to see objects closer than 25 cm because

the focal length of the eye is 25 cm

the distance of the retina from the eye-lens is 25 cm

the eye is not able to decrease the distance between the eye-lens and the retina beyond a limit

the eye is not able to decrease the focal length beyond a limit.

When objects at different distances are seen by the eye, which of the following remain constant?

The focal length of the eye-lens.

The object-distance from the eye-lens.

The radii of curvature of the eye-lens.

The image-distance from the eye-lens.

A person *A* can clearly see objects between 25 cm and 200 cm. Which of the following may represent the range of clear vision for a person *B* having muscles stronger than *A*, but all other parameters of eye identical to that of *A*?

25 cm to 200 cm

18 cm to 200 cm

25 cm to 300 cm

18 cm to 300 cm

The focal length of a normal eye-lens is about

1 mm

2 cm

25 cm

1m

The distance of the eye-lens from the retina is *x*. For a normal eye, the maximum focal length of the eye-lens

=

*x*<

*x*>

*x*=

*x*

A man wearing glasses of focal length +1 m cannot clearly see beyond 1 m

if he is farsighted

if he is nearsighted

if his vision is normal

in each of these cases

An object is placed at a distance u from a simple microscope of focal length f. The angular magnification obtained depends

on f but not on u

on u but not on f

on f as well as u

neither on f nor on u

To increase the angular magnification of a simple microscope, one should increase

the focal length of the lens

the power of the lens

the aperture of the lens

the object size

A man is looking at a small object placed at his near point. Without altering the position of his eye or the object, he puts a simple microscope of magnifying power 5 X before his eyes. The angular magnification achieved is

5

2.5

1

0.2

#### Chapter 19: Optical Instruments Exercise MCQ solutions [Page 431]

When we see an object, the image formed on the retina is

(a) real

(b) virtual

(c) erect

(d) inverted

In which of the following the final image is erect?

(a) Simple microscope

(b) Compound microscope

(c) Astronomical telescope

(d) Galilean telescope

The maximum focal length of the eye-lens of a person is greater than its distance from the retina. The eye is

always strained in looking at an object

strained for objects at large distances only

strained for objects at short distances only

unstrained for all distances

Mark the correct options.

(a) If the far point goes ahead, the power of the divergent lens should be reduced.

(b) If the near point goes ahead, the power of the convergent lens should be reduced.

(c) If the far point is 1 m away from the eye, divergent lens should be used.

(d) If the near point is 1 m away from the eye, divergent lens should be used.

The focal length of the objective of a compound microscope if *f _{o}* and its distance from the eyepiece is

*L*. The object is placed at a distance

*u*from the objective. For proper working of the instrument,

(a)

*L*<

*u*

(b)

*L*>

*u*

(c)

*f*<

_{o}*L*< 2

*f*

_{o}(d)

*L*> 2

*f*

_{o}#### Chapter 19: Optical Instruments solutions [Page 432]

A person looks at different trees in an open space with the following details. Arrange the trees in decreasing order of their apparent sizes.

Tree |
Height(m) |
Distance from the eye(m) |

A |
2.0 | 50 |

B |
2.5 | 80 |

C |
1.8 | 70 |

D |
2.8 | 100 |

An object is to be seen through a simple microscope of focal length 12 cm. Where should the object be placed so as to produce maximum angular magnification? The least distance for clear vision is 25 cm.

A simple microscope has a magnifying power of 3.0 when the image is formed at the near point (25 cm) of a normal eye. (a) What is its focal length? (b) What will be its magnifying power if the image is formed at infinity?

A child has near point at 10 cm. What is the maximum angular magnification the child can have with a convex lens of focal length 10 cm?

A simple microscope is rated 5 X for a normal relaxed eye. What will be its magnifying power for a relaxed farsighted eye whose near point is 40 cm?

Find the maximum magnifying power of a compound microscope having a 25 diopter lens as the objective, a 5 diopter lens as the eyepiece and the separation 30 cm between the two lenses. The least distance for clear vision is 25 cm.

The separation between the objective and the eyepiece of a compound microscope can be adjusted between 9.8 cm to 11.8 cm. If the focal lengths of the objective and the eyepiece are 1.0 cm and 6 cm respectively, find the range of the magnifying power if the image is always needed at 24 cm from the eye

An eye can distinguish between two points of an object if they are separated by more than 0.22 mm when the object is placed at 25 cm from the eye. The object is now seen by a compound microscope having a 20 D objective and 10 D eyepiece separated by a distance of 20 cm. The final image is formed at 25 cm from the eye. What is the minimum separation between two points of the object which can now be distinguished?

A compound microscope has a magnifying power of 100 when the image is formed at infinity. The objective has a focal length of 0.5 cm and the tube length is 6.5 cm. Find the focal length of the eyepiece.

A compound microscope consists of an objective of focal length 1 cm and an eyepiece of focal length 5 cm. An object is placed at a distance of 0.5 cm from the objective. What should be the separation between the lenses so that the microscope projects an inverted real image of the object on a screen 30 cm behind the eyepiece?

An optical instrument used for angular magnification has a 25 D objective and 20 D eyepiece. The tube length is 25 cm when the eye is least strained. (a) Whether it is a microscope or a telescope? (b) What is the angular magnification produced?

An astronomical telescope is to be designed to have a magnifying power of 50 in normal adjustment. If the length of the tube is 102 cm, find the powers of the objective and the eyepiece.

The eyepiece of an astronomical telescope has a focal length of 10 cm. The telescope is focussed for normal vision of distant objects when the tube length is 1.0. m. Find the focal length of the objective and the magnifying power of the telescope.

A Galilean telescope is 27 cm long when focussed to form an image at infinity. If the objective has a focal length of 30 cm, what is the focal length of the eyepiece?

A farsighted person cannot see objects placed closer to 50 cm. Find the power of the lens needed to see the objects at 20 cm.

A nearsighted person cannot clearly see beyond 200 cm. Find the power of the lens needed to see objects at large distances.

A person wears glasses of power − 2.5 D. Is the person farsighted or nearsighted? What is the far point of person without the glasses?

A professor reads a greeting card received on his 50th birthday with + 2.5 D glasses keeping the card 25 cm away. Ten years later, he reads his farewell letter with the same glasses but he has to keep the letter 50 cm away. What power of lens should he now use?

A normal eye has retina 2 cm behind the eye-lens. What is the power of the eye-lens when the eye is (a) fully relaxed, (b) most strained?

The near point and the far point of a child are at 10 cm and 100 cm. If the retina is 2.0 cm behind the eye-lens, what is the range of the power of the eye-lens?

A nearsighted person cannot see beyond 25 cm. Assuming that the separation of the glass from the eye is 1 cm, find the power of lens needed to see distant objects.

A person has near point at 100 cm. What power of lens is needed to read at 20 cm if he/she uses (a) contact lens, (b) spectacles having glasses 2.0 cm separated from the eyes?

A lady uses + 1.5 D glasses to have normal vision from 25 cm onwards. She uses a 20 D lens as a simple microscope to see an object. Find the maximum magnifying power if she uses the microscope (a) together with her glass (b) without the glass. Do the answers suggest that an object can be more clearly seen through a microscope without using the correcting glasses?

A lady cannot see objects closer than 40 cm from the left eye and closer than 100 cm from the right eye. While on a mountaineering trip, she is lost from her team. She tries to make an astronomical telescope from her reading glasses to look for her teammates. (a) Which glass should she use as the eyepiece? (b) What magnification can she get with relaxed eye?

## Chapter 19: Optical Instruments

#### H.C. Verma Concept of Physics Part-1 (2018-2019 Session) by H.C Verma

#### Textbook solutions for Class 12

## H.C. Verma solutions for Class 12 Physics chapter 19 - Optical Instruments

H.C. Verma solutions for Class 12 Physics chapter 19 (Optical Instruments) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Concept of Physics Part-1 (2018-2019 Session) by H.C Verma solutions in a manner that help students grasp basic concepts better and faster.

Further, we at Shaalaa.com provide such solutions so that students can prepare for written exams. H.C. Verma textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 12 Physics chapter 19 Optical Instruments are Light Process and Photometry, Total Internal Reflection, Refraction, Ray Optics - Mirror Formula, Reflection of Light by Spherical Mirrors, Refraction Through a Prism, Refraction by a Lens, Snellâ€™s Law, Concave Mirror, Rarer and Denser Medium, Lensmaker's Formula, Thin Lens Formula, Lenses, The Microscope, Some Natural Phenomena Due to Sunlight, Dispersion by a Prism, Combination of Thin Lenses in Contact, Telescope, The Eye, Power of a Lens, Magnification, Refraction at Spherical Surfaces.

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