Question

A point object is placed midway between two plane mirrors distance ${}^{\prime }{a}^{\prime }$ apart. The plane mirrors form an infinite number of images due to multiple reflections. The distance between $n^{\text{th }}$ order image formed in the two mirrors is

• A. $na$
• B. $2na$
• C. $na/2$
• D. $n^{2}a$

Answer 1

Answer: (B)

The distance of the $n^{\text{th }}$ order image formed by one mirror is at a distance of $(2n-1)\frac{a}{2}$ from the mirror. Distance between the two $n^{\text{th }}$ order images

$=(2n-1)\frac{a}{2}+a+(2n-1)\frac{a}{2}=2na$