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SPHERICAL MIRRORS |
The spherical mirrors are of two types viz concave mirror and convex mirror.
(a) Concave mirror.
The spherical mirror whose reflecting surface is towards the centre C of the sphere of which the mirror forms a part is called concave mirror.
(b) Convex mirror.
In a convex mirror, the reflecting surface is away from the centre C of the sphere of which the mirror forms a part
Some Definitions of the basic features of a concave mirror and a convex mirror.
(1) Centre of Curvature.
It is the centre C of the sphere of which the mirror forms a part .
(2) Radius of Curvature.
It is the radius R of the sphere of which the mirror forms a part.
(3) Pole.
The centre of the spherical mirror is called its pole P.
(4) Principal axis.
It is the line joining the pole and centre of curvature of the mirror.
(5) Aperture.
The diameter of the mirror is called the aperture of the mirror.
The line joining the points A and B represents the aperture of the mirror.
(6) Principal focus.
When rays of light are incident parallel to principal axis then reflected rays lines passes through a fixed point on principal axis. This point is called principal focus.
Or
The point on principal axis through which incident ray lines passes and become parallel after reflection is called principal focus.
Note.
In a concave mirror, all the rays parallel to the principal axis converge to focus F after reflection .For this reason, a concave mirror is known as a converging mirror.
In case of a convex, mirror, all the rays parallel to the principal axis are reflected by the mirror so that they appear to come from focus F behind the mirror. The reflected rays appear to diverge from F .For this reason, a convex mirror is called a diverging mirror.
(7) Focal length.
The distance of principal focus F from the pole P of the spherical mirror is called focal length (f) of the mirror.
PF = f.
PF = f.
IMPORTANT RAY PATHS
there are three rays that are particularly useful in locating the corresponding image point.
(i) When a ray is incident parallel to the principal axis then reflected ray line passes through the focus F.
(ii) The incident ray line passing through focus F is reflected back parallel to the principal axis
(iii) The incident ray line passing through the centre of curvature C is reflected back along its original path
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