Question

Two plane mirrors are parallel to each other and spaced $20cm$ apart. An object is kept in between them at $15cm$ from $A$. Out of the following at which point(s) image(s) is/are not formed in mirror A (distance measured)

• A. $15cm$
• B. $25cm$
• C. $45cm$
• D. $55cm$

Answer 1

The correct option is C $45cm$

The distance between two parallel plane mirror is 20cm

Infinite number of image is formed in this case

Distance of image from mirror A if light first reflects from A is $15+40x$

where x=0,1,2etc

Distance of image from mirror A if light first reflects from B is $15+20\times (2x+1)$

$45=15+40x$

this x is not possible

$45=15+20\times (2x+1)$

$30=20\times (2x+1)$

this x is also not possible

Hence,Option C is answer