An equiconvex lens has a power of $2 \ D$. If it is made of glass of refractive index $1.25,$ then the radius of curvature of each of its surfaces will be $.... \ cm$.

In the displacement method,we use a lens of focal length $f$ and the distance between the object and the screen is $60 \, cm$. $A$ possible value for the focal length is ........ $cm$.

$A$ magnifying lens has a focal length of $10 \, cm$. If an image is to be formed at a distance of $30 \, cm$ from the lens,the object should be placed at a distance of ..... $cm$.

$A$ lens made up of different materials forms two images of a point object $O$ as shown in the figure. Then:

$A$ beam of light converges at a point $P$. Now a lens is placed in the path of the convergent beam $12 \, cm$ from $P$. At what point does the beam converge if the lens is a concave lens of focal length $16 \, cm$ (in $, cm$)?

$A$ thin glass (refractive index $1.5$) lens has an optical power of $-5\,D$ in air. Its optical power in a liquid medium with a refractive index of $1.6$ will be: