Question

How will you differentiate between a convex and a concave lens by looking at

1. a distant object,
2. a printed page?

Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of:

1. object distance, and
2. magnification.

Answer 1

1. On seeing a distant object through the lens, if its inverted image is seen, then the lens is convex, and if the upright image is seen, then the lens is concave.
2. On keeping the lens near a printed page, if the letters appear magnified, then the lens is convex, and if the letters appear diminished, then the lens is concave.

Answer 2

Sr. No.	Basis	Convex lens	Concave lens
1.	Object distance	As long as the item is within the focal length (i.e., closer to the lens than it is to the focal length), the lens will make a virtual image.	When you look at something through a concave lens, the image is always on the same side of the lens as the item, no matter how far away it is.
2.	Magnification	When there is a virtual image (an item within the focal length) and a convex lens, the image stands up and is magnified (magnification > 1).	When you look through a concave lens, the picture you see is always straight up but smaller (magnification < 1).