What is a lens ?

What is lens formula ?

What is lens maker formula ?

What is a double convex lens ?

The radii of curvatures ( R ) of biconvex lens is same. An object is kept at center of curvature. The refractive index of material is n. Lens is kept in air. What is focal length ?

The power of lens is +2.5D . What kind of lens is it ? And what is its focal length ?

What is units of power of lens ?

What is the use of magnifying lens?

What is power of lens ?