Question

Sideways reversal of the image by plain mirror is called
A. Lateral inversion
B. Parallax
C. Optical illusion
D. None of these

Answer 1

Hint: In case of mirrors usually there are three types used. Plain mirror, concave mirror and convex mirror. All will serve different purposes. Properties of different mirrors are different. In case of convex mirrors they always form virtual images. While concave mirrors form both virtual and real images and we will see about plain mirrors.

Formula used:
$\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}$

Complete step by step answer:
In case of convex or concave mirrors the focal length of the mirror determines the type and size of the image formed. Same with the case of plane mirrors also.
$\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}$ This is the mirror formula
Where v is the image distance while u is the object distance and f is the focal length.
But here the focal length of the plane mirror will be infinity. Mathematically the inverse of infinity will be zero. From the above formula we get
$v = - u$
If we consider only the magnitude distance of the object from the mirror will be equal to the distance of image from the mirror and magnification of the mirror will be $\dfrac{{ - v}}{u}$ which is one in this case and it is positive.
Hence if magnification is positive then image formed will be erected and rule is when only one mirror is present and image formed is erected then that image must be virtual. Size of the object will be equal to the size of the image.
Hence an image formed by a plane mirror is always virtually erect and laterally inverted.

In the above image formed due to the plane mirror it is laterally inverted i.e left portion of object becomes right side portion for the mirror.
Since image distance equals the object distance, lateral magnification also will be 1 but inverted laterally.
Hence option A is the answer.

Note:
In case of plane mirrors the magnification is always one i.e size of image will be always equal to size of an object let it be longitudinal size or the lateral size. Real image can never be formed by the plane mirror that’s why the image formed by the plane mirror can’t be caught on the screen.