The plane surface of a plano-convex lens of focal length $f$ is silvered. It will behave as

$A$ bi-convex lens of focal length $10\,cm$ is cut into two identical parts along a plane perpendicular to the principal axis. The power of each lens after the cut is $...........\,D$.

$A$ thin plano-convex lens acts like a concave mirror of focal length $0.2 \ m$ when silvered from its plane surface. The refractive index of the material of the lens is $1.5$. The radius of curvature of the convex surface of the lens will be.......$m$.

The two surfaces of a biconvex lens have the same radii of curvature. This lens is made of glass of refractive index $1.5$ and has a focal length $10 \ cm$ in air. The lens is cut into two equal halves along a plane perpendicular to its principal axis to yield two plano-convex lenses. The two pieces are glued such that the convex surfaces touch each other. If this combination lens is immersed in water (refractive index $= 4/3$), its focal length (in $cm$) is:

$A$ thin convex lens of focal length $25 \, cm$ is cut into two pieces $0.5 \, cm$ above the principal axis. The top part is placed at $(0,0)$ and an object is placed at $(-50 \, cm, 0)$. Find the coordinates of the image.

$A$ plano-convex lens $(f=20 \,cm)$ is silvered at its plane surface. What will be its new focal length (in $\,cm$)?