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The class 12 chapter on Optics (ray and wave) cannot be prepared in a single day. One will definitely need to revise it few times.
Class 12 Physics chapter 9- Ray Optics and optical instruments
Ray Optics and Optical Instruments Chapter 9 from class 12 physics covers reflection, refraction, dispersion along with the help of a diagram of a ray of light. Along with it, students will get to know about image formation of smooth and spherical surfaces with the aid of the fundamental laws of reflection and refraction and how the eye functions. This chapter carries significant weightage in the examination. So, students should pay heed to this chapter.
Ray optics and optical instruments can be studied by subdividing into the following subsections.
- Rectilinear propagation of light- In this section, the rectilinear propagation of light theory is elucidated with the help of a diagram of a ray of light.
- Reflection of light- This chapter is to understand about the reflection of light. Concepts such as deviation, laws of reflection have been covered here. Reflection by a plane surface and a plane mirror is elucidated with the help of diagrams.
- Spherical mirrors- After reading this chapter, students’ knowledge about spherical mirrors will become stronger. Concepts such as paraxial rays are discussed in this chapter. The mirror formula and magnification have been explained step by step.
- Refraction of light- In this section, the following topics are explained broadly so that it becomes easier for students to understand.
-Reflexive index
-Law of Refraction or Snell’s law
-Refraction through a curved surface
-Total internal reflection
-Double refraction from a plane surface
-Single refraction from a plane surface
-The relation between object distance and image distance refraction
-Linear magnification for spherical refracting surfaces.
- Prism- This section deals with the features of a prism, and its various applications. Students will learn about dispersion and deviation of light by a prism.
- Optical instruments- There are many applications of the optical instruments which are discussed in this section. Some of them are:
-Eye: The human eyes have interconnected nerve fibers and cells. The retina has nerve cells like rods and cones and it receives light which then changes it to electrical signals to the brain through the optic nerves. The ciliary muscles aids in the adjustment of the shape and focal length of the lens.
-Simple microscope: A magnifying glass which is a type of a simple microscope is made of converging lens having a small length. A compound microscope is made of two converging lenses, an eyepiece of moderate focal length and large aperture, objective lens with short aperture.
-Telescope: Telescope is used to view objects which are at far distances. A telescope is made of objective lens of large aperture and focal length, and eye lens of small aperture and focal length.
Class 12 Physics chapter 10- Wave optics
In the year 1678, a Dutch physicist propagated the concept of the wave theory of light which explained the causes of reflection and refraction.
Wave front- The source of light is the point which gives disturbance in all directions. Where there is a homogenous medium, the disturbance travels to all the particles of the medium in phase, which are situated at the same distance from the origin of light. Thus, every particle vibrates in phase with each other at all time. Hence, the locus of all the particles of the medium which vibrates in the same phase at all times is known as wave front.
Wavefront can be of the following types:
- Spherical wavefront
- Cylindrical wavefront
Spherical wavefront- A point of a source of light emits a spherical wave front due to the equidistant of the locus of every point from the source.
Cylindrical wavefront- When the source of light is linear like a slit, then it gives a cylindrical wave front.
Plane wave front- A wave front can be called plane when it is a small portion of a spherical or a cylindrical wave front.
Ray of light- The path along which light moves is called as a ray of light. It is also known as wave normal since the rays of light are normal to the wave front.
Huygen’s Principle
Huygen’s principle is a geometrical construction which is beneficial in getting new position of a wave front. In other words, Huygen’s principle talks about how light spreads out in medium.
Principle of superposition
When two or more than two waves overlap each other at a common particle of a medium, then the displacement which takes place is equal to the vector sum of the displacements made by the individual waves.
Solve this question: A short linear object of length b lies along the axis of a concave mirror of focal length f at a distanee u from the pole of the mirror. The size of the image is approximately equal to?
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