Derive the lens formula, `(1)/(f)=(1)/(v)-(1)/(u)` for a concave lens, using the necessary ray diagram.
Two lenses of powers 10 D and -5 D are placed in contact.
(i) Calculate the power of the new lens.
(ii) Where should an object be held from the lens, so as to obtain a virtual image of magnification 2?

Explanation

N//a