Question

The magnification produced by a plane mirror is $+1$. What does this mean?

Answer 1

$m=\frac{h_i}{h_o}=\frac{-v}{u}$

The magnification produced by a plane mirror is +1 which means that size of image formed is exactly equal to the size of the object behind the mirror.
If '$m$' has a magnitude greater than 1 the image is larger than the object, and 'm' with a magnitude less than 1 means the image is smaller than the object.
If '$m$' is positive, the image is erect and if '$m$' is negative, the image is inverted.
Therefore, the magnification of a plane mirror is $+1$ implies, the image formed by the plane mirror is erect and is of the same size as that of the object.