An object is placed beyond the centre of curvature $C$ of the given concave mirror. If the distance of the object is $d_1$ from $C$ and the distance of the image formed is $d_2$ from $C,$ the radius of curvature of this mirror is:

Find the distance of the image from object $O,$ formed by the combination of lenses in the figure:

Curved surfaces of a plano-convex lens of refractive index ${\mu }_1$ and a plano-concave lens of refractive index ${\mu }_2$ have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses

Region $\mathrm{I}$ and $\mathrm{II}$ are separated by a spherical surface of radius $25 \mathrm{cm}$. An object is kept in region $I$ at a distance of $40 \mathrm{cm}$ from the surface. The distance of
the image from the surface is: