Question

how will you determine whether a lens is convex or concave one​

Answer 1

A concave lens is thinner in the middle and thicker at the edges. A convex lens is thicker in the middle and thinner at the edges. Convex and concave lens can also be distinguished by touching them. If the curved surface is bulging outwards then it's convex lens and if the curved surface is curved inwards then it's concave lens.

Answer 2

Explanation:

Convex and concave lens can be distinguished by touching them. If the curved surface is bulging outwards then it's convex lens and if the curved surface is curved inwards then it's concave lens. ... (ii) If the image formed is virtual, erect but diminished, then it is a concave lens.