Paragraph : Two plane mirrors kept at an angle 90∘, as shown in the figure. It is obvious that M1 will form an image of point object O, and M2 will form an image of it. But in practical scenario, a third image is also seen.
The third image formed is :
Now as we have seen that I1 served as an object for M2, or in other words : "light rays coming from I1, fall on M2", these rays will get reflected from M2 and the extrapolation of these reflected rays will give us "the image of I1, in M2"
we can also say that, I2 served as an object for M1, or in other words : "light rays coming from I2, fall on M1", these rays will get reflected from M1 and the extrapolation of these reflected rays will give us "the image of I2, in M1".
It must be the same point where we have I3.
There are two reasons for it :
1.We don’t have a fourth image
2.Symmetry