How many times is the velocity of light in a vacuum compared to the velocity of light in water?

What is the type of the final image,as compared to the object,in the compound microscope?

What is the focal length of a convex lens having power $+5.0 \,D$?

When an object is placed between the principal focus $(F)$ and the pole $(P)$ of a concave mirror,what kind of image is formed?

How will you distinguish between a convex and a concave lens without touching them?

Draw ray diagrams showing the image formation by a convex lens when an object is placed:
$(a)$ Between optical centre and focus of the lens.
$(b)$ Between focus and twice the focal length of the lens.
$(c)$ At twice the focal length of the lens.
$(d)$ At infinity.
$(e)$ At the focus of the lens.