What will be the focal length of a lens whose power is given as $+2.0 \ D$?

Draw ray diagrams showing the image formation by a concave mirror when an object is placed:
$(a)$ Between pole $(P)$ and focus $(F)$ of the mirror.
$(b)$ Between focus $(F)$ and centre of curvature $(C)$ of the mirror.
$(c)$ At centre of curvature $(C)$ of the mirror.
$(d)$ $A$ little beyond centre of curvature $(C)$ of the mirror.
$(e)$ At infinity.

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

At what position should an object be placed in front of a concave mirror to obtain a magnification of $(- 2)$?

If the magnification of a body of size $1\, m$ is $2$,what is the size of the image (in $m$)?

The compound microscope consists of two convex lenses of $5 \, cm$ and $20 \, cm$ focal length. Which of them will be the objective and the eyepiece?