Question

How to determine the signs for v, u and f in numericals (light chapter) for concave and convex mirrors?

Answer 1

f = focal length
u= object distance from pole
v = image distance from pole

for concave mirror all sign for v, u and f is -
for convex - u
+v and +f

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Answer 2

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.