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

$A$ convex lens of focal length $15\,cm$ is placed in front of a convex mirror. When an object is placed at $O$,the image coincides with it. The radius of curvature of the mirror is.....$cm$.

$A$ convex lens of focal length $15 \,cm$ is placed in front of a plane mirror at a distance of $25 \,cm$ from the mirror. Where on the optical axis and from the centre of the lens should a small object be placed such that the final image coincides with the object?

$A$ plano-convex lens of focal length $30\,cm$ has its plane surface silvered. An object is placed $40\,cm$ from the lens on the convex side. The distance of the image from the lens is.......$cm$

An object is placed in front of a symmetrical convex lens with refractive index $1.5$ and radius of curvature $40 \, cm$. The surface of the lens further away from the object is silvered. Under auto-collimation condition,the object distance is.......$cm$.

$A$ concave mirror is placed on a horizontal table with its axis pointing vertically upwards. Let $O$ be the pole of the mirror and $C$ be its center of curvature. $A$ point object is placed at $C$. It forms a real image at $C$. If the mirror is now filled with water,the image will be formed . . . . . .