geometry · Year 6 · AC9M6SP01
Cross-sections of prisms
A cross-section is the flat face you see when you slice through a solid. A prism has the same shape all the way along, so every slice parallel to its base is an exact copy of the base: slice a triangular prism and you get a triangle, slice a hexagonal prism and you get a hexagon. The size never changes either, so the area and the perimeter of every parallel slice match the base. A pyramid is different, because its slices shrink towards the tip. Slices that all match, all the way along, tell you the solid is a prism.
Sample questions
A hexagonal prism is sliced parallel to its base. What shape is the cut face?
- A prism is the same shape all the way along, so every slice parallel to the base matches the base.
- The base is a hexagon.
- Hexagon is the shape of the cut face.
Answer: Hexagon
A pentagonal prism is sliced parallel to its base. What shape is the cut face?
- A prism is the same shape all the way along, so every slice parallel to the base matches the base.
- The base is a pentagon.
- Pentagon is the shape of the cut face.
Answer: Pentagon
A triangular prism is sliced parallel to its base. What shape is the cut face?
- A prism is the same shape all the way along, so every slice parallel to the base matches the base.
- The base is a triangle.
- Triangle is the shape of the cut face.
Answer: Triangle