Measurement
We revise surface area and volume of right prisms and cylinders, then extend to spheres, right pyramids and right cones. We also explore what happens to surface area and volume when any dimension is multiplied by a constant factor k.
11.1 Surface Area & Volume of 3D Solids
- Revise surface area and volume of right prisms and cylinders
- Calculate surface area and volume of spheres, right pyramids and right cones
- Study the effect on volume and surface area when any dimension is multiplied by factor k
- Solve problems involving composite solids
Real-World Connection
A manufacturer designing a tin can needs surface area to know how much metal to buy, and volume to know how much product it holds. Getting these formulas right is worth millions in material savings across a production run of millions of units.
Volume of a right prism
$A_{\text{base}}$ = area of the base (any shape); $h$ = perpendicular height
Surface area of a right prism
$P_{\text{base}}$ = perimeter of base; $h$ = height; 2 bases + lateral faces
Surface area of cylinder
$r$ = radius, $h$ = height; two circular ends + curved surface
Volume of cylinder
Special right prism with circular base: $A_{\text{base}} = \pi r^2$
ℹ️ Note
A cylinder is a right prism with a circular base. Substituting and into the general right-prism formulas gives the cylinder formulas directly: and . Similarly, a cone is a right pyramid with a circular base.
Surface area of sphere
$r$ = radius
Volume of sphere
$r$ = radius
Volume of a right pyramid
$A_{\text{base}}$ = area of base; $h$ = perpendicular height from base to apex
Surface area of a square pyramid
$b$ = base edge length; $l$ = slant height of each triangular face; 1 square base + 4 triangular faces
Volume of cone
Right pyramid with circular base: $A_{\text{base}} = \pi r^2$
Slant height (cone or pyramid)
$l$ = slant height from Pythagoras; $r$ = distance from centre of base to midpoint of base edge (or radius for cone)
Surface area of cone
Base circle + lateral surface; $l$ = slant height
Property / Rule
Effect of scale factor k
If every dimension of a solid is multiplied by k: all lengths scale by k, all areas (surface area) scale by k², all volumes scale by k³.
Worked Example
Triangular prism — surface area and volume
Problem
Worked Example
Cylinder surface area and volume
Problem
Worked Example
Composite solid — cone on cylinder
Problem
Worked Example
Square-based right pyramid
Problem
Worked Example
Effect of scale factor
Problem
CAPS Cognitive Level Distribution