Question

Paragraph : Two plane mirrors are kept at an angle ${90}^{\circ }$, as shown in the figure. It is obvious that M_1 will form an image of point object O, and M_2 will also form an image of it. But a third image is also seen.


The rays after reflection from $M_1$, fall onto $M_2$.This means which of the following :

• A. The image formed in $M_1$ behaves as the object for $M_2$.
• B. The image formed in $M_1$ doesn't behave as the object for $M_2$.
• C. $M_2$ will form infinite number of images for the object O.
• D. $M_2$ can't form an image of object O, in absence of $M_1$.

Answer 1

The correct option is A The image formed in $M_1$ behaves as the object for $M_2$.

Lets model the given scenario as following :

We have an Object and its three images formed by two mirrors. Let's draw the ray diagram as asked in the question.

Now from the diagram we understand that the light ray that incident on mirror $M_2$ ,after reflection from $M_1$, are not incident on the mirror directly from the object O. But if we see the green dotted lines (The extrapolation of reflected rays from $M_1$,which we would draw to locate $I_1$) we can say that the rays are incident on $M_2$ from nowhere but . . . . . . $I_1$. So it means that $I_1$ behaves as an object for $M_2$. Infact if you observe the following diagram

By the same logic we can also state that $I_2$ servs as an object for $M_1$.