C4.1 Geometrical terms
- Syllabus
- 0580–2028–2029
- Topic
- C4.1
- Level
- Core
Learning objectives
Recognise circle parts and simple solids
A geometrical name tells you exactly what a line, region or surface does. For a circle, first locate the centre and decide whether the feature is a distance, a boundary, a straight line or a region.
| Term | Meaning |
|---|---|
| centre | the fixed point equally distant from every point on the circle |
| radius | a line segment from the centre to the circumference |
| diameter | a chord through the centre; its length is twice the radius |
| circumference | the curved boundary of the circle |
| chord | a straight line segment joining two points on the circumference |
| tangent | a straight line touching the circle at exactly one point |
| arc | part of the circumference |
| sector | a region between two radii and an arc |
| segment | a region between a chord and an arc |
A semicircle is half a circle, formed when a diameter splits the circle. For example, if the diameter is 16.8 cm, the radius is 16.8÷2=8.4 cm.
| Solid | Recognition clue |
|---|---|
| cube / cuboid | six flat faces; every cube face is a square |
| prism | the same cross-section all the way through |
| cylinder | two circular ends joined by one curved surface |
| pyramid / cone | surfaces narrow to one apex |
| sphere | one curved surface and no edges |
A face is a flat part of a solid; a surface may be flat or curved; an edge is where two faces or surfaces meet. Thus a square-based pyramid has 8 edges, while a cylinder has curved surface as well as flat circular faces.
Do not call the inside of a circle its circumference: circumference means only the boundary. A chord cuts across the circle at two boundary points; a tangent only touches once. The Core syllabus does not require the term “hemisphere”.