1. Spheres

2. Spheres The figure below shows a sphere.
The point O is called the centre of the sphere.
The distance between any point on the surface of the sphere and its centre (e.g. OA, OB and OC) is called the radius (r) of the sphere.

3. the two parts are identical and each part is called a hemisphere.
centre of the sphere
a hemisphere
If a sphere is divided into two parts by a plane which passes through its centre,
the two parts are identical and each part is called a hemisphere.

4. Volumes of Spheres For any spheres, Refer to the figure on the right.
3 cm
Volume of the sphere
r = 3 cm

5. Follow-up question
Find the volume of a hemisphere with diameter 12 cm. Give your answer in terms of . p
Solution
Radius of the hemisphere
The required volume

6. Surface Areas of Spheres
For any spheres,
Refer to the figure on the right.
9 cm
Surface area of the sphere 2 cm 9 4  = p
r = 9 cm 2 cm
324 p =

7. Follow-up question
Find the radius of a hemisphere with curved surface area cm2. p
Solution
Let r cm be the radius of the hemisphere.
∵ Curved surface area of the hemisphere ∴
∴ The radius of the hemisphere is 10 cm.