Mirror in Optics (Physics)

Mirror:
Surface that reflects most of the light falling on it is called a mirror.

Mirrors are of two types:
1.  Plane
2.  Spherical

(i) Plane mirror: A plane mirror is a flat  surface that produces an erect and virtual image of a real object in which front and back are reversed.
                                                

Light rays from an object strike the surface of a plane mirror. The rays are reflected on the mirror and appear to come from behind the mirror. The reflected rays are drawn as if they are from the image. The image is virtual. Therefore the rays behind the mirror do not exist. They are virtual rays and are represented by dotted lines. The continuous lines from the mirror to the eye indicates the reflected rays. The distance between the object and the mirror is the same as the distance between the image and the mirror.



Characteristics of the image of a plane mirror:
1. VirtualSame 
2. Size as the object 
3. laterally inverted

(ii) Spherical mirror: A Spherical mirror is the portion of a sphere having a reflecting surface. Spherical mirrors form images of real objects in same way as lenses. These are of two types;
1. Convex mirror
2. Concave mirror

Convex mirror: The mirror in which the reflecting surface is formed from the exterior surface i.e., the outer surface away from centre, reflects light.
Concave mirror: A Concave mirror is one in which the reflecting surface is formed from the interior surface of the sphere i.e., the inner surface toward the centre, reflects light.

                    

Important Terms Related to Mirrors:
(i) Centre of curvature (C) : It is the centre of the sphere of which mirror forms a part. It is denoted by 'C'.
(ii) Radius of Curvature (R) : The radius of a sphere of which mirror forms a part  is called radius of curvature.
(iii) Pole : The middle point of the mirror is  called pole of the mirror.
(iv) Principal axis : The line joining centre of curvature to the pole of the mirror is called principal axis.
(v) Aperture : It is the diameter of the circular boundary of the mirror.
(vi) Principal focus : It is a point on the principal axis of the mirror to which incident rays parallel to the principal axis converge (Actually meet at a point) or from which they appear to diverge (Appears to be coming out of that point) after reflection from the mirror. It is clear from the following fig.
         


In case of concave mirror, rays of light after suffering reflection from mirror actually meet at principal focus while in case of convex mirror, they do not meet actually but meet virtually i.e., they appear to be meeting at 'F'.
(vii) Focal length : The distance between the principal focus of a mirror and its pole is called focal length of the mirror. PF is the focal lengths of concave mirror and convex mirror respectively. It is denoted by f.

(viii)Relation between focal length and Radius of curvature

                                                              f  = R/2
                              Radius of curvature = 2 X focal length
i.e., Radius of Curvature is twice the focal length of the mirror.

(ix) Linear magnification :
                                             m = h2 / h1
         where h2 is height of image
           and   h1 is height of object.
                                            m = I / O = -v / u
           I is size of image
          O is size of object
           v  :  distance of image from pole of mirror
           u  :  distance of object from pole of mirror

(x)  Mirror Formula : 

For Concave mirror :     1/u + 1/v = 1/f

For Convex mirror :       1/u + 1/v = 1/f                                 


Courtesy:oocities.org
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R.A.Banwat