Question

how can we observe the lense without touching them?​

Answer 1

There are several ways of finding out if a lens in concave or convex. The simplest way is to hold a convex lens up near the eye and look distant objects through it; then move the lens a little from side to side, the distant object will move in a direction opposite to the movement of the lens. If it is a concave lens then the distant object will move in the same direction as the lens.

The reason is that the convex lens forms an inverted image while the concave lens forms a real image.

Source: Parson's textbook of the eye.....

BRAIN LIEST PLZ

Answer 2

The simplest way is to hold a convex lens up near the eye and look distant objects through it; then move the lens a little from side to side, the distant object will move in a direction opposite to the movement of the lens. If it is a concave lens then the distant object will move in the same direction as the lens.