Question

What is the need for sign convention? Write them.

Answer 1

Sign conventions Rule:

1. All the distance are measured from pole of the mirror as origin.
2. Distance measured in the same direction as that of the incident light are taken as positive.
3. Distance measured against the direction of incident ray is taken as negative.
4. Distance measured upward and perpendicular to the principal axis are taken as positive.
5. Distance measured downward and perpendicular to the principal axis are taken as negative.

Answer 2

Answer:

Explanation:

SIGN CONVENTION - DEFINITION

Sign convention is a set of rules to set signs for image distance, object distance, focal length, etc for mathematical analysis of image formation. According to it:

Object is always placed to the left of lens.

All distances are measured from the optical centre of the mirror.

Distances measured in the direction of the incident ray are positive and the distances measured in the direction opposite to that of the incident rays are negative.

Distances measured along y-axis above the principal axis are positive and that measured along y-axis below the principal axis are negative.

Note: Sign convention can be reversed and will still give the correct results.  

        Convex lens has positive focal length and concave lens has negative focal length.