The optical power of a thin glass lens (refractive index $1.5$) in air is $-5 \ D$. What will be its optical power in a liquid with a refractive index of $1.6$ (in $D$)?

$A$ double convex lens is made of glass of refractive index $1.5$. If its focal length is $30 \ cm$,then the radius of curvature of each of its curved surfaces is:

$A$ lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material of the lens is:

When light rays from the sun fall on a convex lens along a direction parallel to its axis,which of the following statements is true?

The size of the real image produced by a convex lens of focal length $F$ is '$m$' times the size of the object. The image distance from the lens is

$A$ point source of light is moving at a rate of $2 \,cm \,s^{-1}$ towards a thin convex lens of focal length $10 \,cm$ along its optical axis. When the source is $15 \,cm$ away from the lens,the image is moving at: