SPHERICAL MIRROR

The curved surface of a shining spoon could be considered as a curved mirror. The most commonly used type of curved mirror is the spherical mirror. The reflecting surface of such mirrors can be considered to form a part of the surface of a sphere. Such mirrors, whose reflecting surfaces are spherical, are called spherical mirrors.

"Spherical mirrors are mirror in which the reflecting surface is a part of the sphere"

The reflecting surface of a spherical mirror may be curved inwards or outwards

• Concave mirror

A spherical mirror, whose reflecting surface is curved inwards, that is, faces towards the centre of the sphere, is called a concave mirror.

• Convex mirror

 A spherical mirror whose reflecting surface is curved outwards, is called a convex mirror.

Sl. No.	Differentiating Property	Concave Mirror	Convex Mirror
1	Meaning and Other Names	Concave means rounded or hollowed like the interior of a circle or sphere Also called as converging mirror.	Convex means rounded or curved like the exterior of a circle or sphere. Also called as fish eye or diverging mirror.
2	Mirror Shape
3	Structure	The mirror coating of the concave mirror is on the outside of the spherical surface. In concave mirrors, the center of curvature and the reflecting surface fall on the same side of the mirror.	The mirror coating of the convex mirror is on the inside of the spherical surface. In convex mirrors, the center of curvature and the reflecting surface fall on the opposite side of the mirror.
4	Position of the Focus	Focus lies in front of the mirror i.e. focal length is positive.	Focus lies behind the mirror i.e. focal length is negative.
5	Image Properties	The image formed by a concave mirror is real, inverted and enlarged (except when the object is between P and F where the image is virtual, erect and enlarged).	The image formed by a convex mirror is virtual, erect and diminished.
6	Image Projection	An image can be projected on a screen as they are real.	Image cannot be projected on a screen as they are virtual.
7	Usage	They are used in reflecting telescopes, shaving mirrors, torchlights, etc. as they give a magnified image of the objects.	Convex mirrors are used as sideview or rearview mirrors in vehicles as they cover a wider area of view.

Technical terms associated with spherical mirror.

1.      Centre of Curvature

 The centre of curvature of a spherical mirror is the centre of the imaginary hollow sphere of glass, of which the spherical mirror is a part. The centre of curvature is usually denoted by the letter C. The centre of curvature of a concave mirror is in front of it and the centre of curvature of convex mirror is behind the mirrors

2.       Radius of curvature

The radius of curvature of a spherical mirror is the radius of the imaginary hollow sphere of glass, of which the spherical mirror is a part. The radius of curvature is usually denoted by the letter ‘R’.

  3.      Aperture

The portion of a mirror from which the reflection of light actually takes place is called the aperture of the mirror. It is also called linear aperture of the mirror. The aperture of a spherical mirror is denoted by the diameter of its reflecting surface.

 4.      Pole

The centre of the reflecting surface of a spherical mirror is called its pole. It is usually denoted by the letter ‘P’ in each concave and convex mirror. The pole of a spherical mirror lies on the surface of the mirror.

5.      Principal axis 

The principal axis of a spherical mirror is the straight line passing through the centre of curvature C and pole P of a spherical mirror, produced on both sides.

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