Question

What is the lens formula for convex lens with sign and explain also

Answer 1

The following typical equation is used to determine a relation between the focal length of the lens, the distance of object and distance of image. If the focal length is negative, it implies that the lens is concave (diverging), while if positive it implies that the lens is convex (converging lenses)

Answer 2

$\bf{\frac{1}{f} = \frac{1}{v} - \frac{1}{u} }$

Lens Formula is same for both the Lenses.
It doesn't matter which lens we are talking about.

However, the changes come due to difference of sign convention in the lenses.

If object is between Focus and Optical centre of the Lens (1 case), then image formed is virtual and erect.

If object is 'At' or 'before' focus (5 cases), then image is real and inverted.

So,

f = (positive in 5 cases; no Virtual Focus in 1 case)

u = (negative)

v = (positive in 5 cases; negative in 1 case)

So, v and f are what changes the formula from that of concave lens.

NOTE :-

f - Focus
u - Object position
v - Image position