Where is the image formed when an object is placed between the principal focus $(F)$ and the center of curvature $(C)$ of a concave mirror?

Find the focal length of a convex lens,if its power is $+2.0 \ D$. (in $m$)

The distance between the object kept at $2 \, m$ from a plane mirror and its image is $.....$ (in $, m$)

Where should the object be placed to obtain a real and diminished image using a concave mirror?

$A$ student focused the image of a candle flame on a white screen by placing the flame at various distances from a convex lens. He noted his observations:

Observation	Distance of flame from the lens $(cm)$	Distance of screen from the lens $(cm)$
$(i)$	$60$	$20$
$(ii)$	$40$	$24$
$(iii)$	$30$	$30$
$(iv)$	$24$	$40$
$(v)$	$15$	$70$

$(a)$ From the above table, find the focal length of the lens without using the lens formula.
$(b)$ Which set of observations is incorrect and why?
$(c)$ In which case will the size of the object and the image be the same? Give a reason for your answer.

When a concave mirror produces a virtual and magnified image of an object,what is the object distance?