Class -10 Science Physics

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 ~ Some Terms Related To Spherical Mirrors : 

Following are some of the important terms related to spherical mirrors : 

i) Pole of a mirror : The centre of the reflecting curved surface of a spherical mirror is called the pole of the mirror. It is usually represented by letter p. The point p in fig. 4.14 (a) and (b), represents the pole of a concave mirror and a convex mirror. It should be noted that the pole of a spherical mirror is also called vertex of the mirror. 

 

ii) Centre of curvature : It is the centre of hollow sphere of glass of which the spherical mirror forms a part. It is represented by the letter C. 
It should be noted that the centre of curvature is not a part of the mirror. It lies outside its reflecting surface. The centre of curvature of a concave mirror lies in front of it [see Fig. 414 (a)]. However, it lies behind the mirror in case of a convex mirror [see Fig. 4. 14 (b)].

iii) Radius of curvature: The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror. It is represented by the letter R. In Fig. 4. 14. (a) and (b), the distance PC denote the Radius of curvature of the two mirrors. 

iv) Principal axis : The straight line passing through the centre of curvature, C and the pole, P of a spherical mirror is called the principal axis of the mirror. In fig. 4. 14 (a) and (b), the line XY  is the principal axis. The principal axis of a spherical mirror is a fixed line, since the pole, P and the centre of curvature, C are fixed points for a mirror. Remember that principal axis is normal to the mirror at its pole. 

v) Normal : That line joining any point on the mirror to its centre of curvature is called the normal to the mirror at that point. In Fig. 4. 14 (a) and (b) the lines MC, M'C and PC are normals to the mirror at the points M,M' and P, respectively. 

vi) Linear and angular aperture : The diameter of the reflecting surface of a spherical mirror is called its linear aperture. It can also be defined as : 

The length of the straight line joining the points of extremities of a spherical mirror is called its linear aperture. It is show  as the length of the chord MM'  in Fig. 4.14 (a) and (b). 
The angle subtended by the periphery of the spherical mirror (i.e., the extreme points M and M') at the centre of curvature is called angular aperture. In Fig. 4.14  (a) and (b) , the angle MCM' is the angular aperture. The aperture of the mirror denotes its size.


          To  Be  Continued............ 



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