^Image by concave mirror

^Image by concave mirror

As an object approaches the pole of a concave mirror, the size of the image increases, also any kind of image viz. real, virtual, magnified, diminished & of same size is possible. Following is the summary of the various cases of image formation.

1. When an object is placed at ∞, a real, inverted, extremely  diminished image is produced at F.

i.e. for u = ∞, v = f & m < < 1

2. When an object is placed beyond C a real, inverted, diminished image is produced between F & C.

i.e. for ∞ > u > 2 f,  f < v < 2 f & m < 1

3. When an object is placed at C a real, inverted, image having size same as size that of object is produced between F & C.

i.e. for u = 2 f, v = 2 f & m = 1

4. When an object is placed between F & C, a real, inverted, magnified image is produced beyond C.

i.e. for 2 f > u > f, ∞ > v > 2 f & m > 1

5. When an object is placed at F, a real, inverted, magnified image of infinite size is produced at ∞.

i.e. for u = f , v = ∞ & m → ∞.

6. When an object is placed between F & P, a virtual, erect, magnified image of infinite size is produced beyond 2 F on the other side of mirror.

i.e. for f > u > 0, ∞ > v > 0 & m  > 1

Using the image formation rules along with the sign conventions we can explain the various cases of image formation.