Q. (a) Why magnification is taken negative for real images and positive for virtual images?
(b) Why convex mirror is used in rear view mirrors and not concave mirror?
Answers
(a) If image is real, it will be inverted which means height of image will be taken as negative. Also, the height of object is always positive.
Now as magnification = Height of image / Height of object.
Therefore, in case of real image,
Magnification = Height of image (-) / height of object (+)=Negative.
So, Magnification will be negative.
Similarly, if image is virtual, it will be erect.
Therefore, in case of virtual image,
Magnification = Height of image (+) / height of object (+)= Positive
So, Magnification will be positive.
(b) Convex mirror is commonly used in rear view mirrors in vehicles because it gives an erect, virtual, full size diminished image of distant objects with a wider field of view. Thus, convex mirrors enable the driver to view much larger area which is not possible with a concave mirror.