Question

Give the sign convention in concave and convex mirrors.

Answer 1

Sign convention in the case of the concave mirror:

• Since, the object is always placed in front of the mirror hence the sign of the object is taken as negative.
• Since, the center of curvature and focus lie in front of the concave mirror, signs of the radius of curvature and focal length are taken as negative in the case of the concave mirror.
• When an image is formed in front of the mirror, the distance of the image is taken as – (negative), and when the image is formed behind the mirror, the distance of the image is taken as + (positive).
• Height of image is taken as positive in the case of the erect image and taken as negative in the case of the inverted image.

Sign convention in the case of a convex mirror:

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