Question

Explain the sign convention for spherical mirrors.

Answer 1

Sign convention in the case of a concave mirror:
Since the object is always placed in front of the mirror, the sign of object distance is taken as negative.
Since the centre of curvature and focus lie in front of the concave mirror, the radius of curvature and focal length are taken as negative.
When an image is formed in front of the mirror, the distance of image is taken as negative and when the image is formed behind the mirror, the distance of image is taken as positive.
The height of the image is taken as positive in the case of an erect image and taken as negative in the case of an inverted image.

Sign in the case of the convex mirror:
Since object is always placed in front of the mirror hence the sign of object distance is taken as negative.
Since, the centre of curvature and focus lies behind the convex mirror, the radius of curvature and focal length are taken as positive.
In the case of convex mirror, the image is 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.