Title OPTICS.pdf ✅

CLASS IX PHYSICS Introduction: Optics deals with the study of light and electromagnetic waves. Our eyes can see a wave length range from 460 nm to 700 nm in electromagnetic radiation which is called light. Though there was a long debate regarding the light, it is now accepted that light behaves both the (dual nature) particle and wave nature. The phenomena like reflection and reflection can be explained by both Newton's corpuscular theory and Huy- gens wave theory. Photo electric effect is explained by Einstein using particle nature since electrons are parti- cles. Later it was proved that electrons also have dual nature and exhibits its interference and diffraction under certain conditions. In particle nature, light is assumed to travel in straight line with high speed. Speed of light in vacuum is ≃ 3 × 108 m/s. Between two points light travels in a straight line. This path is called ray of light and bunch of rays is called beam of light. Fermat's principal: Lights travels between two points that takes least time. The phenomenon like reflection, refraction and dispersion can be explained using ray approach (Geometrical approach). Reflection of light OPTICS SYNOPSIS - 1
CLASS IX PHYSICS Refraction of light Dispersion of light We shall study the formation of image by plane and spherical reflection, and refracting surface using the basic laws of reflection and refraction. Few general points of geometrical optics: 1. Generally the object is kept on the left hand side of the optical instrument (mirror, lens, etc.) i.e., the ray of light travels from left to right. Sometimes it may happen that the light is travelling in opposite direc- tion. See the fig: 2. In fig (a) and (b) light is travelling from left to right and in fig (c) it is travelling from right to left. 3. Whenever a silvered surface comes as the path of a ray of light it returns from there, otherwise it keeps as moving.

CLASS IX PHYSICS the normal at the point of incident lie in the same plane. • Vector from of law of reflection if ρˆ1 is unit vector along the incident ray ρˆ2, is the unit vector along the reflected ray nˆ is the unit vector along the normal then ρˆ2 = ρˆ1 − 2(ρˆ1nˆ )nˆ Deviation of a ray due to reflection: The angle between the direction of incident ray and reflected ray is called angle of deviation (δ). From the fig. δ = π − (i + r) = π(−2i) (∵ i = r) ∴ δ = π − 2i (or) π − 2r Rotating plane mirror: If the plane mirror is rotated by an angle θ in anti-clockwise order but source is fixed then the reflected ray is turned by angle 2θ in the same order. If the plane mirror is rotated by an angle θ in anti-clockwise order but source is fixed then the reflected ray is turned by angle 2θ in the same order. If the plane mirror is fixed and the incident ray is turned by an angle ' θ ' in clockwise order then the reflected ray turned by an angle θ in anti-clock wise order. Reflected at plane mirror: Image formed due to plane mirror has following properties