 # Physics Revision Notes for Class 12 for Chapter 9 Ray Optics and Optical Instruments

It is through light and our sense of vision that we interpret and know the world around us. Intuitively, there are two things that we can mention about light from our common experience.

First, the enormous speed with which the light travels and second, that it travels in a straight line. It took some time for people to realise that the speed of light was finite and measurable. A light wave can be considered to travel from one point to the other along a straight line joining them. This straight path is known as the ray of light. A bundle of such rays constitutes a beam of light. In CBSE class 12 Physics chapter 9 Ray optics and Optical instruments, we learn about the following concepts:

• Considering the phenomenon of refraction, reflection and dispersion of light using the ray picture of light.
• Image formation by plane and spherical refracting and reflecting surfaces using the basic law of reflection and refraction.
• Construction and working of a few important optical instruments including the human eye.

## CBSE Class 12 Physics Chapter 9 Ray Optics and Optical Instruments

 Thin Lens Formula Laws of Reflection Dispersion in Prism Optical Instruments

## Frequently asked Questions on CBSE Class 12 Physics Notes Chapter 9: Ray Optics and Optical Instruments

Q1

### What is the ‘Thin Lens Formula’?

1/f = (1/v) + (1/u) where, ‘f’ is the focal length (half the radius of curvature), ‘v’ is the distance of the image from the optical centre, ‘u’ is the distance of the object from the optical centre.

Q2

### What does the ‘Law of Reflection’ state?

Law of reflection is defined as: The principle when the light rays falls on the smooth surface, the angle of reflection is equal to the angle of incidence (incident ray, the reflected ray and the normal to the surface all lie in the same plane).

Q3

### What are ‘Optical Instruments’?

Optical instruments are instruments using reflecting and refracting properties of mirrors, lenses and prisms.