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
The question is a very common one.
Magnification is the ratio between the height of the object and the height of the image.
In the case of a real image, the height of the object carries a positive sign while the height of the image carries a negative one.
Hence the magnification is negative.
In case of a virtual image, the height of the image, as well as the height of the object, carries a positive sign.
Therefore, the magnification is positive in this case.
As convex mirror produces virtual and erect image and has a wider field of view whereas, concave mirror produces real and inverted image which makes difficult for the driver to see. Also concave mirror produces enlarged image. That's why convex mirror is used as rear view mirror.
hope this helps you
(a)-sign is used for real image beacuse show the concave mirror
and +sign is used for virtual image beacuse it show the convex mirror
(b)convex mirror is used in rear view mirror because it has wider field of view compare to concave mirror