Question: what is the main structural difference between a convex lens and concave lens?
Answer: In the convex lens, the curve is outward facing, whereas, in the concave lens, the curve faces inward. When the light rays pass through the convex lens, it converges the light rays and focuses on one point. On the other hand, when the light rays go through the concave lens, it diverges the beams, i.e. they spread out.