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SPHERICAL MIRRORS

A mirror whose reflecting surface is a part of an imaginary hollow sphere is known as a spherical mirror.
Spherical mirrors are of two types:
(1) Concave mirrors
(2) Convex mirrors

Concave mirror: It is a spherical mirror whose reflecting surface is towards the centre of the imaginary sphere of which the mirror is a part.

Convex mirror: It is a spherical mirror whose reflecting surface is away from the centre of the imaginary sphere of which the mirror is a part.

Example: The inner shining surface of a steel spoon serves as a concave mirror and the outer shining surface of the steel spoon serves as a convex mirror.

ACTIVITY 1
(1)    Take a large shining spoon. Try to view your face in the inner shining surface of the spoon.
(2)    Bring the spoon close to your face. Observe the image.
(3)    Now move the spoon away from you. Observe the image.
(4)    Now try to view your face in the outer shining surface of the spoon.
(5)    Bring the spoon close to your face. Observe the image.
(6)    Now move the spoon away from you. Observe the image.

Terms related to spherical mirror
(1) Centre of curvature (C)
The centre of curvature of a spherical mirror is the centre of the imaginary hollow sphere of which the spherical mirror is a part.  It is denoted by C.
The centre of curvature is not a part of the spherical mirror. The centre of curvature of a concave mirror lies in front of the spherical mirror and centre of curvature of a convex mirror lies at the back of the mirror.

(2) Pole (P)
The pole of a spherical mirror is the centre of reflecting surface of the mirror. It is denoted by the point P

(3) Radius of curvature (R)
The radius of curvature of a spherical mirror is the radius of the imaginary hollow sphere of which the spherical mirror is a part. It is denoted by R

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

(5) Aperture
The aperture of a spherical mirror is the diameter of the reflecting surface of the mirror

(6) Principal focus of a concave mirror (F)
The principal focus of a concave mirror is a point on the principal axis at which the incident rays parallel to the principal axis after reflection from the concave mirror actually meet at a point on the principal axis.  It is denoted by the letter F

(7) Principal focus of a convex mirror (F)
The principal focus of a convex mirror is a point on the principal axis at which the incident rays parallel to the principal axis after reflection from the convex mirror appears to meet at a point (or appears to diverge from a point)  on the principal axis.  It is denoted by the letter F

(8) Focal Length (f)
It is the distance between the principal focus (F) and pole P of the mirror. It is denoted by letter f.

Relation between focal length (f) and radius of curvature
Provided the aperture of a spherical mirror is much smaller than the radius of curvature, the focal length f can be related to radius of curvature R as


2 comments:

  1. Why did the US place the concave or convex mirror in the North Pole? Is that why the Magnetic field of the earth shifted, causing the Global Warming that we are having?

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