Reflection of light class-10 | www.cbse24.com

Q-What is optics? What are its two main branches?

Ans:-It is the branch of physics which deals with the study of nature, production and propagation of light. The subject of optics can be divided into two main branches.

1. Ray optics 2. wave optics

1.Ray optics or geometrical optics:- It concerns itself with the particle nature of light and is based on

• The rectilinear propagation of light
• The laws of reflection and refraction of light

It explain the formation of image in mirror and lenses ,the aberrations of optical image and the working and designing of optical instruments.

2.Wave or Physical optics:- It concerns itself with wave nature of light and is based on the phenomena like 

• Interference 
• Diffraction 
• Polarization of light

we know that light is an electromagnetic wave in which the electric and magnetic field vary harmonically in space and time. The visible light consists of wave with wavelengths ranging from 4000A° to 7500 A°

Note:-

• Light enables us to see the objects from which it comes as from which it is reflected
• The objects like the sun, other stars, electric bulb ,tube-light ,torch, candle and fire etc. which their own light are called luminous object. Ex:-electric bulb ,tube light ,torch
• Those objects which do not emits light themselves but only reflect the light which falls on them ,are called non luminous objects. Ex-table ,book ,tree

Nature of light:-

There are two theories about the nature of light, wave theory of light and particle theory of light.

According to wave theory:-Light consists of electromagnetic waves which do not require a material medium like(solid ,liquid ,gas) for their propagation.

According to partial theory:-Light is composed of particle which travel in a straight line at very high speed (the element particle that defines light is the photon).

Physics experiments over past hundred year as so have demonstrated that light has a dual nature: light exhibits the particle of both waves and particles(depending on situation it is in). The modern theory of light called "Quantum theory of light "combines both the wave and particle models of light.

Behavior of light at the interface of two media:-

When light traveling in one medium falls on the surface of a second medium, the following three effect may occur.

• A part of the incident light is turned back into the first medium this is called" reflection of light"
• A part of the incident light is transmitted into the second medium along a changed direction. This is called refection of light .
• The remaining third part of light energy is absorbed by the second medium this is called "absorption of light".

Reflection of light:

The process of sending back the light rays which fall on the surface of an object is called reflection of light.

Law of reflection of light:-

• The incident ray ,the reflected ray and the normal(at the point of incidence) all lie in the same plane.
• The angle of reflection is always equal to the angle of incidence.∠i=∠r

Note:-

• When a ray of light falls normally on the surface of a mirror is reflect back along the same path(because the angle of incidence as well as the angle of reflection for such a ray of light are zero)

• The law of reflection of light apply to all kinds of mirror, plane mirror as well as spherical mirror (like concave mirror and convex mirror)
• The above laws of reflection are valid both in case of plane and curved reflecting surface.