What does negative magnification mean in the context of spherical mirrors?

What is the distance between the principal focus and the center of curvature of a spherical mirror?

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

Which of the following can produce a magnification of $+0.5$?

$A$ 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.

The image formed by a lens is due to which optical phenomenon?