Question

How many images are formed for a point object kept in between two plane mirrors ${M_1}$ and ${M_2}$​, at right angles to each other?
A.1
B.2
C.3
D.4

Answer 1

Hint: In this question we will use the direct formula to find the number of images that can be formed at a certain angle. Here, by applying the given value of angle will give us the required result. Further, we will study about the basics of total internal reflection and its applications.
Formula used:
$n = \dfrac{{360}}{\theta } - 1$

Complete step by step solution:
As we know that, if two plane mirrors are placed together on one of their edges so that they form a right angle mirror system, here three images are formed.
$\eqalign{ & n = \dfrac{{360}}{{90}} - 1 \cr
  & \therefore n = 3 \cr} $
Also, right angle mirrors will allow a maximum of two reflections of light from the given object. Here, as the angle decreases, even more than three reflections can occur.
Therefore, the correct option is C), i.e., there will be 3 images that can be seen at the given value of angle.

Additional information:
As we know, total internal reflection or TIR effect is the phenomenon in which the reflection of the entire incident light is off the boundary. Total Internal Reflection only takes place when the following two conditions are together followed:
 1. Light has to travel from denser medium to rarer medium but not vice-versa.
2. Critical angle of the medium: The Angle of incidence must be greater than the critical angle of medium ${\theta _c}$ ​.
The below diagram shows the two conditions of Total Internal Reflection i.e., TIR:

There are some of the places where TIR or total internal reflection is seen. Some of them are mentioned following:
1. In Diamond: here, when the incident ray falls on the face of the diamond such that the angle formed by this ray is greater than the critical angle. Here, we can observe that the critical value of the diamond is ${23^\circ }$. This condition is responsible for the total internal reflection in diamond. Therefore the diamond shines.
2. Mirage: since, mirage is an optical illusion which is responsible for the appearance of the water layer at short distances mainly in a desert. Mirage is also an example of total internal reflection which occurs due to atmospheric refraction.
3. Optical fiber: in optical fire when the incident ray falls on the cladding, it suffers total internal reflection because the angle formed by the ray is greater than the critical angle. Nowadays Optical fibers are used because it has revolutionized the speed with which signals are transferred, not only across cities but across countries and continents making telecommunication one of the fastest modes of information transfer.

Note:
We should know the difference between reflection and refraction. Reflection is the change of the direction of wave or light to back to its original medium whereas, in refraction light slightly bends towards the normal when the medium is changed.