why magnification is taken negative for real image and positive for virtual image, explain
Answers
As per the new Cartesian convention, distances above the optical axis are taken as positive and distances below the optical axis are taken as negative.
Magnification is the ratio of the height of the image to the height of the object.
In case of a real image, the image is inverted and hence the height of the image has a negative sign, while the height of the object has a positive sign.
⇒⇒ The magnification negative.
In case of a virtual image, the image is erect and hence the height of the image has a positive sign. The height of the object also has a positive sign.
⇒⇒ The magnification positive.
If concave mirrors are used a rear view mirrors in vehicles instead of convex mirrors, the images of the objects beyond the focal length would be inverted. We are not used to seeing inverted images.
Further, the nearer objects, between the focal length and twice the focal length, would be magnified. This would make it very difficult for us to see clearly the objects that are farther away.
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 (+)= PositiveSo, Magnification will be positive.