Question

please give me answer of two questions given below

Answer 1

In the first question answer will be between focus and the center of the lens(that is between f and o) . A virtual image cannot be obtained on the screen as it forms behind the lens.

In the second question I m unable ro understand BT perhaps its answer is that if the F1 is focal length then F2 much be the center of curvature. In a lens it is a compulsion for the focal length of both the sides (+ve and -ve) be same hence in this case F1 and F2 are the focal lenghts of a lens on either side. In can be both concave and convex lens.

HOPE SO IT WOULD HELP!!