Two vertical parallel mirrors A and B are separated by 10 cm. A point object O is placed at a distance of 2 cm from mirror A. The distance of the second nearest image behind mirror A from the mirror A is ______ cm.

Two parallel mirrors A and B are separated by 10 cm. Object O is 2 cm from mirror A (hence 8 cm from mirror B).

Images behind mirror A:

1st image (I₁): Direct reflection in A → 2 cm behind A.

2nd image (I₂): Object at 8 cm from B creates image at 8 cm behind B, which is at 10 + 8 = 18 cm from A (behind mirror A when viewed from the object side).

3rd image: I₁ (at 2 cm behind A = 12 cm from B) reflects in B → image at 12 cm behind B = 22 cm from A.

The images behind A in order of distance: 2 cm, 18 cm, 22 cm, ...

The second nearest image behind mirror A is at 18 cm.