Concave Mirrors

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Slide 1: 

Ray Diagrams of Concave Mirrors

Introduction : 

Introduction The theme of this unit has been that we see an object because light from the object travels to our eyes as we sight along a line at the object. Similarly, we see an image of an object because light from the object reflects off a mirror and travel to our eyes as we sight at the image location of the object. From these two basic premises, we have defined the image location as the location in space where light appears to diverge from. Ray diagrams have been a valuable tool for determining the path of light from object to mirror to our eyes

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Images Formed by a Concave Mirror

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To understand the basic principles of Ray optics To understand the principles of “Construction” of ray diagrams To explain how the images are formed by the concave mirrors for various positions of objects Objectives

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Spherical Mirrors are Portions of spherical surfaces If the outside of the spherical mirror is silvered, then it is called a concave mirror Concave Mirror Basic Principles

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Pole (P) (C) Centre of Curvature The Line Passing through C,P – Principal Axis Terms Used in Spherical Mirrors P – Pole C – Centre of Curvature Principal Axis Geometrical Centre Centre of the sphere of which the mirror is a part

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Construction

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Principal Axis Construction 1 F Ray Parallel to Principal Axis Rule 1. The Ray Parallel to Principal Axis is reflected through the Principal Focus ‘F’

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F Principal Axis Construction 2 Ray Passing through ‘F’ Rule 2. Ray Passing through the principal focus ‘F’ is reflected parallel to the Principal Axis .

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F Principal Axis C Construction 3 Rule 3. The ray passing through the Centre of Curvature ‘C’ is reflected through the same path.

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Images Formed ...

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F C 1. Object at Infinity... All the Rays of the Object at infinity are parallel to Principal Axis and hence according to Construction 1 the image is formed at ‘F’. ... image at 'F'

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2.Object Beyond 'C'... F C There are two rays emerging from the object which is placed beyond ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point between ‘F’ and ‘C’ where the image is formed. ... image between 'F' and 'C' 1 2

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3.Object at 'C'... F C There are two rays emerging from the object which is placed at ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘F’. Both the rays meet at the point ‘C’ where the image is formed ... image at 'C' 1 2

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F C 4.Object between 'F' and 'C'... There are two rays emerging from the object which is placed between ‘F’ and ‘C’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point beyond ‘C’ where the image is formed. ... image beyond 'C' 2 1

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F C 5.Object at 'F'... There are two rays emerging from the object which is placed at ‘F’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the point of infinity. ... image at infinity 2 1

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F C 6.Object between 'P' and ‘F'... There are two rays emerging from the object which is placed between ‘P’ and ‘F’. One ray is parallel to Principal Axis and the other ray passes through ‘C’. Both the rays meet at the back of the mirror when the rays are extended. The virtual image is formed at the back of the mirror. ... image at the back of the mirror P 1 2

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P C F Object @ Infinity – Image @ ‘F’ – Real, Inverted Object beyond ‘C’ – Image between ‘F’ & ‘C’- Real, Inverted Object @ ‘C’ – Image @ ‘C’ – Real, Inverted. Object between ‘F’ & ‘C’ – Image beyond ‘C’ – Real, Inverted Image …All in One (Recap)

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When the Object moves closer to the Mirror, The Image Moves away from the Mirror The Relative Movement of 'Object' & 'Image'.

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Ready Reckoned..

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Used in search light, car lights and telegraphic intermittent lights. Used in mirror telescopes (its front is a silver-plated mirror) The spherical concave mirror finds its most valuable application as eye mirror (Helmholtz 1851). It serves during examination of the inside of eyes.

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ray of light which is directed towards the principal focus of a convex mirror, after reflection will emerge parallel to the principal axis. A ray of light incident obliquely to the principal axis, towards the pole of the mirror gets reflected according to the laws of reflection. A convex mirror always gives a virtual image irrespective of the position of the object. Convex Mirror

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