Calculate the following : (i) location of the image (ii) height of the image (iii) nature of the image Solution: (i) For a convex mirror, focal length is positive. Sometimes a negative lens is used for a beam expander for a laser and no focus is formed The diverging lens does not form a real image, but a virtual one, and thus is negative. Notice that rule 1 means that the radius of curvature of a spherical mirror can be positive or negative. In diagram, PF is the focal length of the mirror. The image distance \(d_i\) is positive for real images and negative for virtual images. 1 Verified Answer. NCERT Books. Focal length of plane mirror is positive or negative Ask for details ; Follow Report by Tvfaisal2368 29.06.2019 Log in to add a comment The concave mirror will form a real image, so by convention it's focal length is positive. The object is placed on the left of the mirror. Distances measured on the other side are negative. Focal length. The answer you get seems to depend on how you "make" your plane mirror as the limit of a convex or concave mirror. Whether the focal length of a concave mirror is taken as positive or negative depends on the convention being followed. Any distances measured on that side are positive. ... A plane mirror is placed in between , so that the two virtual image so formed coincide . BNAT; Classes. BOOK FREE CLASS; COMPETITIVE EXAMS. Principal section. What does a positive or negative image height or image distance mean? The focal length \(f\) is positive for concave mirrors and negative for convex mirrors. Determining the focal length of a concave mirror and the convex lens for a distant object. According to cartesian system focal length of a concave mirror is negative whereas radius of curvature of convex mirror is positive. A concave mirror has a +ive focal length, and as you make it more and more flat, the focal point moves away from the surface. Class 1 - 3; Class 4 - 5; Class 6 - 10; Class 11 - 12; CBSE. As per the New Cartesian sign convention, 1. Example 6: A 1.4 cm long object is placed perpendicular to the principal axis of a convex mirror of focal length 15 cm at a distance of 10 cm from it. It is represented by the symbol f. For mirrors of small aperture, f=R/2. The limit is a flat mirror with a focal point at +infty. To figure out what the signs mean, take the side of the mirror where the object is to be the positive side. View Answer. The distance between the pole and the principal focus of the mirror, is called the focal length of the mirror. Focal length is defined as the distance between the center of the lens or mirror and the focal point of the lens or the mirror . 2. f, the focal length, is positive for a concave mirror, and negative for a convex mirror. If the plane mirror is at a distance of 24 cm from the object , find the radius of curvature of the convex mirror . 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