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NCERT Solutions for Class 8 Maths Chapter 10 : Visualising Solid Shapes

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Chapter 10 : Visualising Solid Shapes

10.1 Introduction

In Class VII, you have learnt about plane shapes and solid shapes. Plane shapes have two measurements like length and breadth and therefore they are called two-dimensional shapes whereas a solid object has three measurements like length, breadth, height or depth. Hence, they are called three-dimensional shapes. Also, a solid object occupies some space. Two-dimensional and three-dimensional figures can also be briefly named as 2-D and 3- D figures. You may recall that triangle, rectangle, circle etc., are 2-D figures while cubes, cylinders, cones, spheres etc. are three-dimensional figures.

10.2 Views of 3D-Shapes

You have learnt that a 3-dimensional object can look differently from different positions so they can be drawn from different perspectives. For example, a given hut can have the following views.Why is the top view of the glass a pair of concentric circles? Will the side view appear different if taken from some other direction? Think about this! Now look at the different views of a brick.
Observe different things around you from different positions. Discuss with your friends their various views.

10.3 Mapping Space Around Us

You have been dealing with maps since you were in primary, classes. In Geography, you have been asked to locate a particular State, a particular river, a mountain etc., on a map. In History, you might have been asked to locate a particular place where some event had occured long back. You have traced routes of rivers, roads, railwaylines, traders and many others.
How do we read maps? What can we conclude and understand while reading a map? What information does a map have and what it does not have? Is it any different from a picture? In this section, we will try to find answers to some of these questions. Look at the map of a house whose picture is given alongside.
What can we conclude from the above illustration? When we draw a picture, we attempt to represent reality as it is seen with all its details, whereas, a map depicts only the location of an object, in relation to other objects. Secondly, different persons can give descriptions of pictures completely different from one another, depending upon the position from which they are looking at the house. But, this is not true in the case of a map. The map of the house remains the same irrespective of the position of the observer. In other words, perspective is very important for drawing a picture but it is not relevant for a map.
From this map, can you tell –
(1) how far is Raghav’s school from his house?
(2) would every circle in the map depict a round about?
(3) whose school is nearer to the house, Raghav’s or his sister’s?

10.4 Faces, Edges and Vertices

Each of these solids is made up of polygonal regions which are called its faces; these faces meet at edges which are line segments; and the edges meet at vertices which are points. Such solids are called polyhedrons.
How are the polyhedrons different from the non-polyhedrons? Study the figures carefully. You know three other types of common solids.
Convex polyhedrons: You will recall the concept of convex polygons. The idea of convex polyhedron is similar.
Regular polyhedrons: A polyhedron is said to be regular if its faces are made up of regular polygons and the same number of faces meet at each vertex.



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