What is the power of a convex lens with a focal length of $50 \ cm$?

For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram.

How many centres of curvature does a lens have?

The power of a lens is $5$ dioptre. What is the focal length of the lens (in $m$)?

What is the expression for magnification of a lens?

$A$ concave lens made of a material of refractive index $n_{1}$ is kept in a medium of refractive index $n_{2}$. $A$ parallel beam of light is incident on the lens. Complete the path of rays of light emerging from the concave lens if
$(i)$ $n_{1} > n_{2}$ $(ii)$ $n_{1}=n_{2}$ $(iii)$ $n_{1} < n_{2}$