Question

write different between convex and concave

Answer 1

When parallel rays of light pass through a concave lens the refracted rays diverge so that they appear to come from one point called the principal focus. ... The difference between concave lenses and convexlenses is their respective property to diverge and converge light rays.

Answer 2

concave lens.
The reflecting surface of the concave mirror is bulged inwards.
Concave lens can be identified as the lens which disperses the light rays around, that hits the lenses.

convex lens.
But the reflecting surface of the convex mirror is bulged outward.
Convex lens refers to the lens which merges the light rays at a particular point, that travels through it.