Question

If two solid hemispheres of same base radius r are joined together along their bases, then the curved surface area of this new solid is ______.

• A. $4\pi r^2$
• B. $6\pi r^2$
• C. $2\pi r^2$
• D. $12\pi r^2$

Answer 1

The correct option is A $4\pi r^2$


The curved surface area of a hemisphere of radius 'r' is $2\pi r^2$.
Here, we join solid hemispheres along their bases of radius r, from which we get a solid sphere.
Hence, the curved surface area of new solid
$=2\pi r^2+2\pi r^2=4\pi r^2$