write 3 difference between concave and convex lens?
indhu15 has given absolutely correct answer. So, you can refer to it.
Here are few more things I like to add,
Convex lenses are curved outward and they cause light that goes trough it to converge or concentrate on one point. Think of a magnifying glass that is used to burn something. The light that goes through it concentrates on a point so you can burn things. Concave lenses are curved inward and when light goes through it diverges or spreads out. Think of a flashlight. The light comes from a small bulb goes through it and spreads out to a bigger beam on the other side.
Hope this helps,
@indhu15. Good answer. You get a thumb up. Keep posting!!