Two plane mirrors are placed making an angle θ in between them. Write an expression for the number of images formed if an object is placed in between the mirrors. State the condition, if any.

There are two cases possible:

Case 1 — If angle θ° between the mirrors is such that

n = 360\over θ

1. the number of images is n, when the object is placed asymmetrically between the mirrors.
2. the number of images is n – 1, when the object is placed symmetrically (i.e., on the bisector of the angle) between the mirrors.

Case 2 — If n = 360\over θ is even, the number of images is always n – 1 for all positions of object in between the mirrors.