A visual proof of - Curved surface area of a hemisphere = 2(Area of circle)

Question

Suppose we have a circle with radius $r$ .
So its area is $\pi r^2$.
Now suppose we have a hemisphere of the same radius ie. $r$.
Then its curved surface area is $2 \pi r^2$.
Which means it is equal to two times that of the circle.I need a visual proof for that.

Answer 1

Make it into two steps. First, use parallel projection, to bring your hemisphere to the hemicilinder. You should show that parallel projeection does not change area (use the fact that while the height decreases, the width increases by the same ratio).

The hemicilinder in turn is composed of rectangles, with a small piece of the equator as base, and $r$ as height. The circle is equally composed of triangles, same base and height, so you get that the hemicilinder has double area than the circle.