The distance between object and its two times magnified real image as produced by a convex lens is $$45 \mathrm{~cm}$$. The focal length of the lens used is _______ cm.

Two immiscible liquids of refractive indices $$\frac{8}{5}$$ and $$\frac{3}{2}$$ respectively are put in a beaker as shown in the figure. The height of each column is $$6 \mathrm{~cm}$$. A coin is placed at the bottom of the beaker. For near normal vision, the apparent depth of the coin is $$\frac{\alpha}{4} \mathrm{~cm}$$. The value of $$\alpha$$ is _________.

A bi convex lens of focal length $$10 \mathrm{~cm}$$ is cut in two identical parts along a plane perpendicular to the principal axis. The power of each lens after cut is ____________ D.