Question

The two plane mirrors are inclined at an angle of 120°. If object is placed on the bisector line between the mirrors the
number of images formed are
(A) 4
(B) 3
(C) 1
(D) 2.​

Answer 1

Explanation:

Given: An object is kept between two plane mirrors inclined at an angle 120 from each other

To find the ratio of number of images which are formed if the object is not on the bisector and on the bisector

Solution:

If there are two plane mirrors inclined to each other at an angle θ, the number of images of a point object formed are determined as follows:

If (

θ

360

∘

) is odd integer (say m) number of images formed

n=m, if the object is not on the bisector of mirrors

n=(m–1), if the object is on the bisector of mirrors.

So, when θ=120

∘

, we get

m=

120

360

=3

So,

number of images which are formed if the object is on the bisector

number of images which are formed if the object is not on the bisector

=

3−1

3

=

2

3