If I convert 10 V, 1 ampere to 5 V, do I get 5 V 2 ampere?
If you use a linear regulator, no. You get 5 V, 1 A.

If you use a buck converter, not quite. The converter is not 100% efficient. Maybe you get 8.5 or 9 W out, so 5 V, 1.7 or 1.8 A.