Chapter-9|Ray Optics and Optical Instrument|NCERT 12th Physics:
Optics:
It is the branch of Physics, which deals with the study of propagation of light. The subject of optics can be divided into two main branches.
(I) Rays optics
(II) Wave optics
(I) Rays Optics(Geometrical Optics): It deals with practical nature of light and is based on
(a) The rectilinear propagation of light i.e light ray travel in straight line.
(b) The law of reflection and refraction of light.
(II) Wave Optics(Physical Optics): It concerns itself with the wave nature of light and it is based on the phenomena like
(a) Interference
(b) Diffraction and
(c) Polarisation of light.
Reflection of Light:
Reflection is the phenomenon of change in the path of light without any change in the medium.
The returning back of light in the same medium from which it has come after striking a surface is called reflection of light.
Laws of Reflection:
The laws of reflection are are as given below.
(I) The angle of incidence is equal to the angle of reflection i.e ∠i= ∠r
(II) The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.
Note: (I) The above laws of reflection are valid both in case of plane and curved reflecting surfaces.
(II) For normal incidence ∠i=0, therefore ∠r= 0.