Synopsis

Part 1  :

• The mirrors which have Spherical surface are known as spherical mirrors.

*  In a spherical mirror if the bulged surface is made smooth for reflection and the inner surface is silvered, then the mirror is called convex mirror.

*  In a spherical mirror if the inner surface is made smooth for reflection and the bulged surface is silvered, then the mirror is called concave mirror.

• The midpoint (Geometrical centre) of the mirror is called pole (P) of the mirror.

*  The centre of the sphere, from which the mirror is assumed to be made, is the centre of curvature of the mirror.

*  The line, which passes through the centre of curvature and pole is called principal axis/central axis of the mirror.

*  The rays coming parallel to principal axis, after reflection meets at a point or seems to be coming from a point on the principal axis. This point is known as focus (F) of the mirror.

*  The distance between pole and centre of curvature is known as the radius of curvature (R) of the mirror.

*  The distance between pole and focus of the mirror is known as the focal length (f) of the mirror.

*  Relation between f and R is f = R/2 or R = 2f.

*  The distance of the object from the pole of a mirror is known as object distance (u).

*  The distance of the image from the pole of a mirror is known as image distance (v).

*  The rays which are very near to the principal axis are called paraxial rays.

 

Part 2  :

• The ratio of size of image to the size of object is known as linear magnification.

         

Magnification (m) = 

                                         

 m =

 

 

         Mirror formula :

 

• Sign convention to be followed while using mirror formula 

      * All distances should be measured from the pole.

      * The distances measured in the direction of incident light to be taken  as positive and  measured in the opposite direction of incident light to  be taken as negative.

      * Height of object and height of image are positive if measured upward from the axis and negative if measured downward.

• Rules for image tracing (concave mirror)

      * All the rays that are parallel to the axis get reflected such that they pass through the focal point of the mirror.

     *  An incident ray that goes through the focal point of the mirror will,  when reflected, travel parallel to the axis.

     * An incident ray that is normal to the surfaces (passing through centre of curvature), on reflection will travel along the same ray but in the  opposite direction.

*  Real image : An image formed by the actual intersection of reflected light rays is called a real image. It can be formed on the screen.

*  Virtual image : The image formed by the intersection of extended reflected rays   is called a virtual image. It cannot be formed on a screen.

*  Rules for image tracing (convex mirror)

    * A ray running parallel to axis, on meeting the convex mirror, will get reflected so as to appear as if it is coming from the focal point.

    *   An incident ray going in the direction of the focal point, after reflection will become parallel to main axis.

    *  An incident ray going in the direction of centre of curvature will, on  reflection, get back in opposite direction and looks that it is coming  from the centre of curvature.

      *  Nature of images when object is kept at different places before a concave  mirror

     

  *  Convex mirrors are used as rear view mirrors for all types of vehicles.

 * Concave mirrors are used as shaving mirrors, used by dentists and also used in solar heaters / cookers etc.