In order to produce an image with magnification m, a concave mirror of focal length f is used. If the object is kept at a distance d from the mirror, then equals
STEP 1: Given data
In a concave mirror
The object's distance from the mirror pole i.e. u (since object is placed on the left side of mirror, hence distance is taken as negative)
The focal length of the concave mirror is always negative.
(The distance calculated in the direction of the incident ray is taken as positive and the opposite direction is taken as negative.)
STEP 2: Finding the position of the image
Using the mirror formula,
The image distance from the mirror i.e. .
STEP 3: Finding the magnification
Using the magnification formula in the mirror
STEP 4: Putting the values in the expression given
Replacing the expression on RHS with v;
Since
Therefore, the correct option is (A).