$A$ convex lens made of glass (refractive index $= 1.5$) has a focal length of $24 \ cm$ in air. When it is totally immersed in water (refractive index $= 1.33$),its focal length changes to: (in $cm$)

$A$ glass concave lens is placed in a liquid in which it behaves like a convergent lens. If the refractive indices of glass and liquid with respect to air are $^a{\mu _g}$ and $^a{\mu _l}$ respectively,then

The focal length of a biconvex lens made of glass with equal radii of curvature is $f$. If the lens is dipped in water, what will be its new focal length? (Take the refractive index of glass as $3/2$ and water as $4/3$)

Radii of curvature of a converging lens are in the ratio $1 : 2$. Its focal length is $6 \,cm$ and refractive index is $1.5$. Then its radii of curvature are ......... respectively.

The height of the image formed by a converging lens on a screen is $8\,cm$. For the same position of the object and screen,another image of size $12.5\,cm$ is formed on the screen by shifting the lens. The height of the object is...

The sun subtends an angle of $0.5^{\circ}$ at the earth's surface. Its image is formed by a convex lens of focal length $50 \ \text{cm}$. The diameter of the image will be (in $\text{mm}$)