Refraction of Light

Magnification is the ratio of the size of the image (h_I) to the size of the object (h_o)

i.e.,

Magnification produced by a lens can be equal to one, greater than one or less than one depending upon the size and nature of the image.

Case I

When, height of the image (h_I) = height of the object (h_o)

Thus, when the magnification is one, the size of the image is equal to the size of the object.

Case II

When h_I > h_o

Case III

For both type of lenses, the height of the object is always positive, while the height of the image may be + or - depending upon its nature.

As per sign convention for lenses, the height of an inverted and real image is negative and hence the magnification of a lens is negative when it produces an inverted and real image. For an erect and virtual image, the height of the image is positive. So, the magnification is positive when an erect and virtual image is formed.