Where is the image formed when an object is placed at the principal focus $(F)$ in front of a convex lens?

The refractive indices of turpentine oil,kerosene,and alcohol are $1.47, 1.44$,and $1.36$ respectively. Based on this information,complete the following ray diagrams to show the path of a ray of light through each medium. (Give a reason for your answer.)

In an astronomical telescope,how is the focal length of the objective lens compared to the focal length of the eyepiece?

When a plane mirror is rotated through a certain angle,the reflected ray turns through twice as much and the size of the image

Give the mathematical expression for the power of a lens.

Can a plane mirror be called a spherical mirror?