An object is placed symmetrically between two plane mirrors, inclined at an angle of 72°, then the total number of images observed is

Question

An object is placed symmetrically between two plane mirrors, inclined at an angle of 72°, then the total number of images observed is (A) 5 (B) 4 (C) 2 (D) Infinite

Tardigrade Admin · Accepted Answer

For number of images formed from plane mirror

m = \frac{360}{θ} = \frac{360}{72} = 5

If it was at any other point the number of images

(n) = m

but this is not so.
Since it is placed symmetrically :

n = m - 1

or

n = 5 - 1

or

n = 4

images

Q. An object is placed symmetrically between two plane mirrors, inclined at an angle of 72∘, then the total number of images observed is

5

4

2

Infinite

For number of images formed from plane mirror m=θ360​=72360​=5 If it was at any other point the number of images (n)=m but this is not so. Since it is placed symmetrically : n=m−1 or n=5−1 or n=4 images

Q. An object is placed symmetrically between two plane mirrors, inclined at an angle of $7 2^{\circ}$ , then the total number of images observed is

For number of images formed from plane mirror
$m = \frac{360}{θ} = \frac{360}{72} = 5$
If it was at any other point the number of images $(n) = m$ but this is not so.
Since it is placed symmetrically :
$n = m - 1$
or $n = 5 - 1$
or $n = 4$ images