Question

say me the sign convention for concave, convex mirror. And for concave,convex lens

Answer 1

concave and convex has same Cartesian rules.
1. object should be placed on the left of the mirror.
2. distance measured from left side are taken as negative and distance measured from the right are taken as positive.
3. height above the principal axis are taken as positive.
4. height below the principal axis are taken as negative

Answer 2

                         Note :

• f = focal length

• v = distance of image .

• u = distance of object .

Lens formula :

1 / f = 1 / v - 1 / u

Concave lens :

f = negative

u = negative

v =  negative

Convex lens

f = positive

u = negative

v = positive for real image ,

v = negative for virtual image .

The optical centre is chosen as the origin of the coordinate system.

With respect to optical centre :

The part which are above are positive, below negative.

The part which are right are positive while left is negative.

This is just like the normal x-axis and y-axis in the co-ordinate system .