Question

An object is placed symmetrically between two plane mirrors inclined at an angle of ${72}^{\circ }$, then the total number of images observed will be

• A. $5$
• B. $4$
• C. $3$
• D. $2$

Answer 1

The correct option is B $4$


Hence total number of images formed will be $4$.

Alternative:
Given:
Angle between the mirrors, $\theta ={72}^{\circ }$
So, $n=\frac{{360}^{\circ }}{\theta }=\frac{{360}^{\circ }}{{72}^{\circ }}=5$
As $n$ is odd and object is placed symmetrically (i.e.; the object is placed at the equal distance from each mirror in between them or in other words object is placed at the line of symmetry in between the two mirrors), hence, the number of images,
$N=n-1=5-1=4$.