Page 2 - WS3

6. Compare the length of two threads used in wrapping.

Observation

1. The length of the thread used to cover the cylinder is two times more than the
length of the thread used to cover the hemisphere.

2. Curved surface area of the hemisphere = x curved surface area of cylinder
=
=
= (i.e h = 2r because height of the
cylinder = diameter of sphere)
Total surface area of sphere = 2x

Result
Surface area of a sphere = (verified experimentally).

Learning Outcome
Students will derive the formula for surface area of a sphere through an activity.

Activity Time
Let the radii of a sphere and of the base of a cylinder are same. Find the ratio of the
curved surface area of a sphere to curved surface area of a cylinder if the height of the
cylinder is 2 times of its radius.