Question

Two plane mirrors are initially inclined at 30° to each other and they move apart with an addition of 30° till the angle becomes 120°. The object is in between and equidistant from the mirrors. Find the sum of all the images formed. (Mirrors are inclined symmetrically).

• A. 20
• B. 21
• C. 22
• D. 23

Answer 1

The correct option is B

21

We have a formula by which we can calculate the number of images formed:

n = ($\frac{{360}^{\circ }}{\theta }$-1)

n = ($\frac{{360}^{\circ }}{{30}^{\circ }}$-1) + ($\frac{{360}^{\circ }}{{60}^{\circ }}$-1) + ... + ($\frac{{360}^{\circ }}{{120}^{\circ }}$-1)

n = 11 + 5 + 3 + 2 = 21