A hemisphere is exactly half of a sphere, formed when a sphere is cut through its center. It has a curved (rounded) surface and one flat circular base.
1. Curved Surface Area (CSA) of a hemisphere with radius r is half the surface area of a full sphere = 2πr²
2. Plain (base) Surface Area is the area of the flat circular base = πr²
3. Total Surface Area (TSA) = CSA + Plain SA = 2πr² + πr² = 3πr²
4. For a hemisphere, TSA ≠ CSA because, unlike a full sphere, it has a separate flat base.