Now u = PO should be taken as negative and f = PF and v = PI should be taken as positive (as per Cartesian co-ordinate system set up at P as the origin and the axis of the mirror as the X-axis).

Note :

(i) In using Cartesian co-ordinate system sign convention, the object distance (real object) is always negative.

(ii) Similarly virtual image distance is always positive and real image distance is always negative.

(iii) Focal length of concave mirror is negative and that of convex mirror is positive.

(iv) Light is always incident from left to right.

(v) The formula is applicable to concave, convex and even plane mirror. For plane mirror the radius of curvature is a , therefore the focal length is also infinite and hence

Linear magnification : m

It is defined as the ratio of the height of image (h₂) to the height of the object,

Note : (i) For real object h₁ > 0, u < 0
(ii) For real image h₂ < 0, v < 0
(iii) For virtual image h₂ > 0, v > 0
(iv) For plane mirror

(v) For concave mirror

Index

Light

16.1 Laws of Reflection at plane surfaces
16.2 Mirrors
16.3 Laws of Refraction at plane surfaces, Refractive Index and Critical Angle
16.4 Refraction at curved spherical surfaces and Lens maker’s formula
16.5 Lenses
16.6 Refraction in Prisms, Prism Formula
16.7 Dispersion of Light, Angular Dispersion and Dispersive Power
16.8 Optical Instruments and Magnifying Power

Chapter 17