Question

Two plane mirrors $\text{A}$ and $\text{B}$ are parallel to each other and spaced $20\text{cm}$ apart. An object is kept between them at $15\text{cm}$ from $\text{A}$. Following are the distances of the image formed by mirror A(from it). Which of the following is not possible?

• A. $15\text{cm}$
• B. $25\text{cm}$
• C. $45\text{cm}$
• D. $55\text{cm}$

Answer 1

The correct option is C $45\text{cm}$


For plane mirror, we know that,

$\text{object distance = image distance}$

Using above concept, we can get

$\to$ First image formed in mirror $\text{A}$ is $\text{OA}$ at $15\text{cm}$ from mirror $\text{A}$

$\to$ Image formed in mirror $\text{B}$ at a distance $\text{OB}$ will act like a virtual object and its image is formed in mirror $\text{A}$ at $(5\text{cm}+20\text{cm})=25\text{cm}$

$\to$ Image $\text{OA}$ will act like a virtual object for mirror $\text{B}$. Its image in mirror $\text{B}$ will form at $=35\text{cm}$

$\to$ Now the image of $O_A$ in mirror $\text{B}$ will act like the virtual object for mirror $\text{A}$.

Therefore, its image in mirror $\text{A}$ will be formed at $(35\text{cm}+20\text{cm})=55\text{cm}$

Alternative:


The first three images will be at a distance $15\text{cm}$, $25\text{cm}$ and $55\text{cm}$ from mirror A.

Hence option (c) is correct choice.