CBSE Important Questions Ch 9 Class 12 Physics 2025 PDF

Ray optics is also called geometrical optics. This is the study of the nature of light and how it moves as rays, unlike wave optics, where characteristics of light are considered in terms of waves. Light is therefore taken in its simplest form as straight lines. This method is very useful in the explanation of the working of different optical devices such as mirrors, lenses, microscopes, telescopes, etc. The concepts of ray optics should be very well known to the students of Class 12 who are studying Physics if they want to score well in their exams. 

Chapter 9 contains various topics that are asked every year in board examinations. In Class 12 Physics Chapter 9 Important Questions, you are going to study various topics like spherical mirrors, snells’s law, TIR, refraction at a spherical surface, lens maker’s formula, refraction through a prism, optical instruments, etc. Here, the important questions of ray optics and optical instruments and primary concepts related to this topic will be discussed to help the students prepare for their exams.

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In the table given below, we have provided the links to Ray Optics and Optical Class 12 Physics Important Questions PDFs. You can download them without having to share any login info.

Refraction and Snell’s Law

Concept Overview 

Refraction is a situation where there is a change in the speed as well as in the direction of light passing from one medium to another. The situation can be very well described by Snell's Law, which can be written as:

sin i / sin r = v1 / v2 = n2 / n1

Important Questions:

1. State and explain Snell’s Law of refraction. Derive the relation for the refractive index of a medium.
2. A ray of light passes from air into water with a refractive index of 1.33. If the angle of incidence is 30°, calculate the angle of refraction.
3. Explain the phenomenon of total internal reflection. Under what conditions does it occur?

Lenses and Mirrors: Reflection and Refraction

Concept Overview 

Lenses and mirrors are the two very important aspects of ray optics. A mirror forms an image due to the reflection of light, while a lens does so by the refraction of light. Concave and convex are the two major types of mirrors, and convex and concave are the two major types of lenses.

• Concave Mirror: Converges light rays to come together to one point.
• Convex Mirror: Diverges light rays.
• Concave Lens: Diverges light rays.
• Convex Lens: It converges light rays together.

Important Questions:

1. Derive the mirror equation and explain the terms involved.
2. An object is placed 10 cm in front of a concave mirror of a focal length of 15 cm. Calculate the position of the image formed.
3. Describe the construction of a convex lens and derive its lens formula.
4. An object is placed at the focus of a convex lens. What type of image is formed? Explain with the help of ray diagrams.

Image Formation by Mirrors and Lenses

Concept Overview 

Mirrors and lenses form either real or virtual images based on the position of the object concerning the focal point. Characteristics, size, and positioning are determined by curvature, focal length, and the distance of the object from a mirror or lens.

Important Questions:

1. Discuss the image formation by a concave mirror for different object positions (beyond 2f, at 2f, between f and 2f, at f, and within f).
2. What is the difference between a real image and a virtual image? Give examples of each type using mirrors and lenses.
3. Describe the image formed by a convex lens when an object is placed at different positions compared to the focal length. Illustrate using ray diagrams.

Power of a Lens

Concept Overview 

The power of a lens is defined as the reciprocal of its focal length. This is measured in diopters (D). The formula for the power is:

P = 1 / f

If the focal length is positive, it is a converging lens, which means convex. A negative focal length means that the lens is diverging, hence concave.

Important Questions:

1. Define the power of a lens. If a lens has a focal length of 20 cm, calculate its power.
2. A person with a near point at 80 cm requires corrective lenses. If the near point for a normal eye is 25 cm, what should be the focal length of the corrective lens?
3. Two lenses of focal lengths 10 cm and 20 cm are placed in contact. Find the focal length of the combination.

Refraction Through a Prism

Concept Overview 

A prism refracts light based on its refractive properties. The angle of deviation Delta is defined as the angle between the incoming and refracted rays. You can express the relationship between the angle of deviation, the angle of incidence, and the prism's refractive index using the prism formula.

Delta = (i + e) - A

Important Questions:

1. Derive the formula for the angle of deviation in a prism.
2. What is the refractive index of a material of the prism if the minimum deviation angle is 30° and the prism angle is 60°?
3. Explain the phenomenon of dispersion of light using a prism.

The Human Eye and its Defects

Concept Overview 

The human eye serves as an optical instrument that generates an image on the retina. It can see distant objects because of the accommodation provided by the lens. However, some defects of the eye cause vision defects, which include the following:

• Myopia or nearsightedness: The defect is corrected using a concave lens.
• Hypermetropia or Farsightedness: It is corrected by using convex lenses.
• Astigmatism: This arises from an abnormal curvature of either the cornea or lens.

Important Questions:

1. Explain the structure of the human eye and the working of its different parts.
2. What is myopia? Briefly discuss some of its common causes, treatment, and preventive measures.
3. What is hypermetropia? How does it get corrected through lenses?
4. Explain the defects of vision and their correction using appropriate optical devices.

Optical Instruments: Microscopes and Telescopes

Concept Overview 

Optical instruments such as microscopes and telescopes use lenses and mirrors to enlarge images of small objects or of distant celestial bodies. Their working depends upon the principles of refraction along with the properties of convex and concave lenses.

Compound Microscope: A compound microscope uses two lenses, namely, the objective lens and the eyepiece. It enlarges the image of an object near the objective lens better.

Astronomical Telescope: An astronomical telescope also uses two lenses, one of which is the objective lens and the eyepiece to magnify distant objects in space.

Important Questions:

1. Describe how a compound microscope works. Derive the expression for the total magnification of a microscope.
2. What is the difference between an astronomical telescope and a compound microscope?
3. Derive the expression for the magnifying power of a telescope.

Ray optics is a very interesting and essential part of the Class 12 Physics syllabus. Proper understanding of all key concepts, such as refraction, lenses, mirrors, the human eye, and optical instruments, is crucial to achieving excellence in the subject. Concentrating on these basic concepts and solving important questions on ray optics and optical instruments listed can improve the understanding of ray optics among students and lead to good results in the exams. In addition, it is also important for students to be good at drawing ray diagrams, as they are very important for visualising and solving problems in this chapter of Physics. Regular practice and review of these core topics will boost confidence and contribute to success in Class 12 Physics.We hope that you practice the above Class 12 Physics Chapter 9 Important Questions and achieve your dream marks.All the best!