Question

Two plane mirrors are inclined at angle of 40° between them. Number of images seen of a tiny object kept between them is ______.

Options

• Only 8

• Only 9

• 8 or 9

• 9 or 10

Answer 1

Two plane mirrors are inclined at angle of 40° between them. Number of images seen of a tiny object kept between them is 8 or 9.

Explanation:

The number of images depends upon the angle between the mirrors and where it is placed. It can be obtained as follows:

n = `(360^circ)/theta`

Here, θ = 40°

∴ n = `(360^circ)/40^circ`

∴ n = 9

n we got is an odd number, so according to rule, again two cases exist,

1. When object is placed asymmetrically, then, 

n = `(360^circ)/theta`

Here, θ = 40°

∴ n = `(360^circ)/40^circ`

∴ n = 9

2. When an object is placed symmetrically,

n = `(360^circ)/theta - 1`

∴ n = `(360^circ)/40^circ - 1`

∴ n = 9 - 1

∴ n = 8