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Page 1 of 9, , LIGHT REFLECTION & REFRACTION, Light is a form of energy, which gives us the power of vision.,  Ray of light : It is a line in the direction of movement of light.Beam of light : It is bucnh of rays of, light.,  Parallel beam: All the rays are parallel., Reflection of Light, When the light is allowed to fall on highly polished surface, such as mirror, most of the lightgets, reflected., Laws of Reflection, , 1. The angle of incidence is always equal to angle of reflection., , 2. The incident ray, reflected ray and the normal to the reflecting surface at the, point ofincidence lie in the same plane., Image formed by Plane Mirror (Plane reflecting surface), , 1. Virtual (imaginary) & Erect : The image that do not form on screen.Real, images can be recorded on the screen., , 2. Laterally inverted (The left side of object appear on right side of image), 3. The size of image is equal to that of object., 4. The image formed is as far behind the mirror as the object is in front of it., , Reflection of light by spherical Mirrors, Mirrors, whose reflecting surface are curved inward or outward spherically are called spherical, mirror., For example - Spoon, , The curved surface of shinning spoon can be considered as curved, , mirror., If it is curved inward, If it is curved outward, , Act as concave mirror, Act as a convex mirror., , --- PAWAN SIR, , 1 / 19

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Page 2 of 9, Few Basic terms related to Spherial Mirror, , 1. Principal axis: Line joining the pole and centre of curvature of the spherical mirror., 2. Pole: The geometrical central point of the reflecting spherical surface. (aperture),denoted, by (P)., , 3. Aperture: The width of reflecting spherical surface., 4. Centre of curvature : The centre of the hollow glass sphere of which the sphericalmirror, is a part is called as centre of curvature., , 5. Radius of curvature : The distance between the pole and the centre of curvature. i.e., PC = R or The radius of the hollow sphere of which the mirror is a part., , 6. Focus point : The point on the principal axis, where all parallel rays meet after reflectionis called, as Principal Focus or Focus. It is denoted by letter ‘F’., , 7. Focal length : The distance between the pole and focus point i.e. PF = f, 8. Relationship between focal length and Radius of curvature., Image Formation by Spherical Mirror, Before we learn the formation of image or ray diagram, let us go through few tips, (a) Remember, a ray of light which is parallel to principle axis always pass through focus(meet, at focus) or vice-versa., (b) A ray of light which passes through centre of curvature (it is also known as normal at thepoint of, incidence on spherical mirror) will retrace their path after reflection., (c) A ray of light falling on pole get reflected at the same angle on the other side of principalaxis., Note : A ray of light passes through centre of curvature of reflecting spherical surface alwaysact as, normal at the point of incidence. If we know the normal we can draw angle of incidence and angle, of reflection., , --- PAWAN SIR, , 2 / 19

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Image Formation by Concave Mirror : The ray diagrams given in NCERT Books, Image formation by Convex Mirror: The ray diagrams given in NCERT Books, Uses of Concave Mirror, 1 Used in torches, search light and headlight of vehicle., , 2. Used to see large image of face as shaving mirror, 3. Used by dentist to see large images of the teeth, 4. Large concave mirror used to focus sunlight (heat) in solar furnaces., Uses of Convex Mirror, Used as rear-view mirror in vehicles because it gives erect image. Italso helps the driver toview large, area., Sign Convention for Reflection by Spherical Mirror, , 1. The object is always placed to the left side of mirror., 2. All distance should be measured from pole (P); parallel to principal axis., 3. Take 'P' as origin. Distances measured, Right of the origin (+x-Axis) are taken positive, Left of the origin (–x-Axis) are taken negative, Perpendicular to and above principal axis (+y-Axis) are taken positive, Perpendicular to and below principal axis (–y-Axis) are taken negative, , --- PAWAN SIR, ., , 3 / 19

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Mirror Formula, , f, , distance between F and Pole, , v, , distance of image from Pole, , u, , distance of object from Pole, , R, , distance between centre of curvature and pole., , Where, Magnification, It is expressed as the ratio of the height of the image to height of the object., , From 1 and 2 equation, When, , image height from principle axis., , Object height from principle axis, , Few tips to remember sign convention for Spherical mirror :, f, , u, , CONCAVE, , -ve(real), , -ve(real), , CONVEX, , +ve, , +ve, , v, -ve(real), +ve(virtual), +ve, , h – is always +ve, h´ – is +ve for virtual , –ve for Real., , --- PAWAN SIR, ., , 4 / 19

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Refraction of Light, Happens in Transparent medium when a light travels from onemedium to another, refraction takes, place., A ray of light bends as it moves from one medium to another Refraction is due to change inthe speed, of light as it enters from one transparent medium to another., Speed of light decreases as the beam of light travel from rarer medium to the denser medium., Some Commonly observed phenomenon due to Refraction, Your eyes., Rainbows., Light bending in a glass of water., Glasses., Camera lenses., Object dislocation in water., Binoculars., Refraction through a Rectangular Glass slab:, When a incident ray of light AO passes from a rarer medium, (air) to a denser medium (glass) at point. O on interface KL, it, will bends towards the normal. At ptO1, on interface NM the, light ray entered from denser medium(glass) to rarer medium, (air) here the light ray will bend away from normal O O’ is a, refracted ray O B is an emergent ray. If the incident ray is, extended to C, we will observe that emergent ray O1B I parallel, to incident ray. The ray will slightly displaced laterally after, refraction., Note : When a ray of light is incident normally to the interface of two media it will go straight,, without any deviation., Laws of Refraction of Light, The incident ray, the refracted ray and the normal to the interface of two transparent mediaat the, point of incidence, all lie in the same plane., The ratio of sine of angle of incidence to the sine of angle of refraction is a constanti.e., , --- PAWAN SIR, ., , 5 / 19

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For given colour and pair of media, this law is also known as Snell’s Law, Constant n is the refractive index for a given pair of medium. It is the refractive index of thesecond, medium with repect to first medium., , Refractive Index, The refractive index of glass with respect to air is given by ratio of speed of light in air to thespeed of, light in glass., , c, , Speed of light in vacuum =, , speed of light in air is marginally less,, , compared to that in vacuum., Refractive index of air with respect to glass is given by, , Refractive index of water, Refractive index of water, Spherical Lens, A transparent material bound by two surfaces, of which one or both surfaces are spherical,forms a lens., Convex lens, , Concave lens, , 1. Bulging outwards, , 1. Bulging inwards., , 2. Converging lens., , 2. Diverging lens., --- PAWAN SIR, ., , 6 / 19

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Concave Lens, A lens bounded by two spherical surfaces, curved inwards is known asdouble concave lens, (or simply concave lens), It is also known as diverging lens because it diverges the light., Few Basic Terms Related to Spherical Lens, , 1. Centre of curvature : A lens, either a convex lens or a concave lens is combination of two, , spherical surfaces. Each of these surfaces forma part of sphere. The centre, of these two spheres are called centre of curvature represented by C1 and, C2., , 2. Principal axis :, 3. Optical Centre :, , Imaginary straight line passing through the two centres of curvature, The central point of lens is its optical centre (O). A ray of light, when, passes through 'O' it remains undeviated i.e. it goes straight., , 4. Aperture : The effective diameter of the circular outline of a spherical lens., 5. Focus of lens : Beam of light parallel to principal axis, after refraction from, , , Convex lens, converge to the point on principal axis,, , denoted by F, known as Principal focus., , , , Concave lens, appear to diverge from a point on the, , principal axis known as principalfocus., , , , The distance OF2 and OF1 is called as focal length., , Sign Convention for Refraction by Spherical Lens, Similar to that of spherical mirror, only the difference is that all the measurement are made from, optical centre 'O', , --- PAWAN SIR, ., , 7 / 19

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Lens formula, , Magnification, It is defined as the ratio of the height of image to the height of object., , It is also related to ‘u’ & ‘v’, , From equation (1) & (2), If magnification, m > 1, then image is magnified, m = 1 , image is of same size, m < 1, image is diminished, Few Tips to Remember Sign Convention for Spherical Lens, f, , u, , CONCAVE, , -ve, , -ve, , CONVEX, , +ve, , -ve, , v, -ve(virtual image always), +ve(real), -ve(virtual), , h is always +ve, h´ = –ve for Real and +ve for Virtual &Errect., Power of Lens, The degree of convergence or divergence of light ray achieved by a lensis known as power ofa lens., It is defined as the reciprocal of its focal length Represented by P., If F is given in meter, then, , --- PAWAN SIR, ., , 8 / 19

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If F is given in cm , then, , SI unit of power of a lens is “diopter” denoted by ‘D’, 1diopter or 1D, , It is the power of lens whose focal length is 1 m, , , , Power of convave lens or diverging lens is always negative, , , , If any optical instrument has many lens, then net power will be, , --- PAWAN SIR, ., , 9 / 19