Page 201 - ICSE Math 8

(a) Convex polyhedron (b) Concave polyhedron
Fig. 18.10

Prism

A polyhedron whose side faces are parallelograms and bases are congruent parallel polygons is called a prism.
Figure 18.11 shows some terms associated with a prism.

D¢

E¢
O¢
C¢
A¢ Lateral face
B¢ Axis and length

Base D Lateral edge
E Height
O C
A F
B
Fig. 18.11: Oblique prism

E¢ D¢
The various types of prisms are:
(a) Right Prism: If the lateral edges of a prism are perpendicular to its A¢ C¢
bases, a prism is called a right prism (Fig. 18.12). B¢
In a right prism: E D
(i) Length = height A C

(ii) All the lateral faces are rectangular. B
Fig. 18.12
(iii) All the lateral edges are equal to the height of the prism.
(iv) Number of lateral edges = number of lateral faces = number of sides in the base
C¢
(b) Oblique Prism: A prism in which the lateral faces are parallelograms is known
as an oblique prism. O
The prisms are further classified based on the number of sides in the bases as: A¢ B¢

(a) Triangular Prism: If the bases of a prism are triangles, a prism is called Axis
a triangular prism (Fig. 18.13).
C
In a triangular prism, there are 6 vertices and 9 edges, 2 triangular bases and 3
lateral faces. O¢
A B
Point to remember Fig. 18.13
A triangular prism whose lateral edges are perpendicular to its bases is called a right triangular prism.
The lateral faces of a right prism are bounded by rectangles.

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