Question

Two plane mirrors are parallel to each other and an object $O$ is placed between them. The distance (in $\text{cm}$) of the first three images formed by the mirror $M_2$, from the mirror $M_2$ will be :

• A. $5,10,15$
• B. $5,15,30$
• C. $5,25,35$
• D. $5,15,25$

Answer 1

The correct option is C $5,25,35$


The object is at a distance of $5\text{cm}$ from $M_2$, thus first image will form at $5\text{cm}$ from $M_2$. Also, object is at a distance of $10\text{cm}$ from $M_1$, so image $\left(A\right)$ formed by it will be at $10\text{cm}$ from it. This image $\left(A\right)$ will act as object for $M_2$ and second image will be form at $25\text{cm}$ from $M_2$. Similarly, the first image of object in $M_2$ will act as object for $M_1$. Its image $\left(B\right)$ in $M_1$ will form at $20\text{cm}$ from it. This will again act as object for mirror $M_2$ and third image will form at $35\text{cm}$ from it.

Alternative:

The first three images will be at a distance $5\text{cm}$, $25\text{cm}$ and $35\text{cm}$ from mirror $M_2$