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| Spherical Mirrors |
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| A mirror whose polished, reflecting surface is a part of a hollow sphere of glass or plastic is called a spherical mirror. |
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| In a spherical mirror, one of the two curved surfaces is coated with a thin layer of silver followed by a coating of red lead oxide paint. Thus, one side of the spherical mirror is opaque and the other side is a highly polished reflecting surface. In a diagram the opaque side of a mirror is always shown shaded. |
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| In the diagrams given here, please remember that the opaque, non reflecting side is shaded grey. The reflecting side is black. |
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| Depending upon the nature of the reflecting surface of a mirror, the spherical mirror is classified as: |
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 Concave mirror |
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Convex mirror |
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| Concave Mirror |
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| Concave mirror is a spherical mirror whose reflecting surface is towards the
center of the sphere of which the mirror is a part. |
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| Convex Mirror |
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| Convex mirror is a spherical mirror whose reflecting surface is away from the
center of the sphere of which the mirror is a part. |
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| Concave and Convex Mirror |
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| Let us now define certain physical terms relating to spherical mirrors. |
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| Center of Curvature is the center of the sphere of which the spherical mirror forms a part. It is denoted by the letter C. |
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Center of Curvature |
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| Radius of Curvature is the radius of the sphere of which the mirror is a part. It is represented by the letter R. |
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| Radius of Curvature |
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| Linear aperture is the distance between
the extreme points (X and Y) on the periphery of the mirror. |
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| XY is the Aperture |
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| Pole is the midpoint of the aperture of the spherical mirror. It is represented by the letter P. |
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| Midpoint of xy |
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| Principal axis is the straight line passing through the pole and the
center of curvature of a spherical mirror. |
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| Principal Axis |
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| Secondary axis is any other radial line passing through the
center of curvature other than the principal axis. |
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| Secondary Axis |
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| The normal at any point of the spherical mirror is the straight line obtained by joining that point with the
center of the mirror. The normal at point A on the mirror is the line AC obtained by joining A to the
center of curvature of the mirror. Normal at any point on a spherical mirror is equal to the radius of the sphere of which the mirror is a part. |
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| Normal |
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| The rays of light parallel to the principal axis of a mirror after reflection, either pass through a point (in case of a concave mirror) or appear to diverge from a point (in the case of a convex mirror) on the principal axis and this point is referred to as the principal focus or focal point of the mirror. |
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| The principal focus of a spherical mirror may be defined as a point on its principal axis where a beam of light parallel to the principal axis converges to or appears to diverge from after reflection from the spherical mirror. |
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| Focal length is the distance between the pole and the focus of a mirror. It is represented by the letter f. |
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| Characteristics of Focus of a Concave and a Convex Mirror |
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