Question

which sign conventions are used while solving sums based on convex Mirrors
example what value we should take for focal length while solving sums on convex Mirrors

Answer 1

Sign convention in the case of a convex mirror:

• Since, object is always placed in front of the mirror hence the sign of object is taken as negative.
• Since, the centre of curvature and focus lies behind the convex mirror, so sign of radius of curvature and focal length are taken as + (positive) in the case of convex mirror.
• In the case of convex mirror, image always formed behind the mirror, thus the distance of image is taken as positive.
• In the case of a convex mirror, always an erect image is formed, thus the height of image is taken as positive.

f, the focal length, negative for a convex mirror.

A convex mirror has a radius of 20 cm. An object is placed 30 cm in front of the mirror. Determine where the image will appear. Since the radius is 20 cm (which is the distance from the mirror to the centre), and since the focal point is half ways in between and negative for a convex mirror, f = -10 cm.