Question

Assertion: Magnification of plane mirror is 1.
Reason: The image formed by a plane mirror is as far behind the mirror as the object is in front of it.
A. Both assertion and reason are correct and reason is the correct explanation of the assertion.
B. Both assertion and reason are correct but reason is not the correct explanation of the assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Answer 1

Hint: Magnification is described as the ratio of the image distance with the object distance. Mathematically this relation is expressed as $m = \dfrac{v}{u}$ where $m$ is the magnification of the image, v is the image distance and u is the object distance. A plane mirror follows the laws of reflection and forms and image that has the following characteristics:
a. The image formed is virtual.
b. The image formed is of the same size.
c. The image is laterally inverted.
d. The image is erect.
e. The image is formed at an equal distance from the mirror as of the object.

Complete answer:
In terms of the distance of the object and its image, magnification is expressed as $m = \dfrac{v}{u}$ where $m$ is the magnification of the image, $v$ is the image distance and $u$ is the object distance.
Given that $m = 1$ ,
Hence, $m = \dfrac{v}{u} = 1$
$ \Rightarrow v = u$
This implies that the image distance is equal to the object distance in magnitude.
So, both assertion and reason are correct and reason is the correct explanation of the assertion.

Hence, option A is the correct answer.

Note: Lateral inversion means that the object and image are mirror images of each other. If you stand facing a mirror and raise your left hand; your image will raise your right hand. Lateral inversion by any measure does not mean that the image gets shifted. The image remains intact.