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Two types:
a) Concave mirror
b) Convex Mirror
To understand image formation we shall follow the Cartesian sign convention. According to this convention, all distances are measured from the pole of the mirror or the optical centre of the lens. The distances measured in the same direction as the incident light are taken as positive and those measured in the direction opposite to the direction of incident light are taken as negative. The heights measured upwards with respect to x-axis and normal to the principal axis (x-axis) of the mirrors/ lenses are taken as positive. The heights measured downwards are taken as negative.
For a convex mirror, the reflected rays appear to diverge from a point F on its principal axis. The point F is called the principal focus of the mirror. If the parallel paraxial beam of light were incident, making some angle with the principal axis, the reflected rays would converge (or appear to diverge) from a point in a plane through F normal to the principal axis. This is called the focal plane of the mirror.
The distance between the focus F and the pole P of the mirror is called the focal length of the mirror, denoted by f. We now show that f = R/2, where R is the radius of curvature of the mirror.
(Concave mirror)
(Convex mirror)
Following is the mirror equation can be used for both concave and convex mirrors:
(Symbols have their usual meaning)
The size of the image relative to the size of the object is another important quantity to consider. We define linear magnification (m) as the ratio of the height of the image (hi) to the height of the object (ho).
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