Ray Optics and Optical Instruments Class 12 Notes Chapter 9
Introduction
Nature has endowed the human eye(retina) with the sensitivity to detect electromagnetic waves within a small range of the electromagnetic spectrum.
light
Electromagnetic radiation belonging to this region of the spectrum( wavelength of about 400 nm to 750 nm) is called light.
It is mainly through light and the sense of vision that we know and interpret the world around us.
There are two things that we can intuitively mention about light from common experience.first, that it travels with enormous speed and second that it travels in a straight line. It took some time for people to realise that the speed of light is finite and measurable.which presently accepted value in vacuum is c= 2.99792458×10^8 m/s. for many purposes,it suffices to take c=3×10^8 m/s. The speed of light in vacuum is the highest speed attainable in nature.
Ray of light
A light wave can be considered to travel from one point to another,along straight line joining them.the path is called a ray of light.
Beam of light
bundle of such rays constitutes a beam of light
Reflection of light by spherical Mirrors
Low of Reflection
- The angle of reflection equals to angle of incidence.
- The incident ray,reflected ray and the normal to the reflecting surface at the point of incidence lie in the same plane.
these laws are valid at each point on any reflecting surface whether plane or curved.
Sign convention
According to this convention all distances are measured from the pole of the mirror or the optical centre of the lens.The distances measured in the same direction as the incident light are taken as positive and those measured in the direction opposite to the direction of incident light are taken as negative.
Focal length of spherical mirrors
Focal length
The distances between the focus F and the pole P of the mirror is called the focal length of the mirror.
Focal length is denoted by f.
formula of focal length , f = R/2
Prove that f= r/2 for a concave/convex mirror?
proof :-
Let
