Question

A right circular cylinder just encloses a sphere of radius r.

Find curved surface area of the cylinder.

Answer 1

Just encloses means radius of sphere and cylinder will be same and height of cylinder would be equal to the diameter of the sphere.

i.e.

Radius of cylinder = $r$

Height of cylinder = $2r$

Therefore, Curved Surface area of the cylinder = $2\pi rh=2\pi r\times 2r$ = $4\pi r^2$