CHAPTER 13
SURFACE AREAS AND VOLUMES
13.1 Introduction
Wherever we look, usually we see solids. So far, in all our study, we have been dealing
with figures that can be easily drawn on our notebooks or blackboards. These are
called plane figures. We have understood what rectangles, squares and circles are,
what we mean by their perimeters and areas, and how we can find them. We have
learnt these in earlier classes. It would be interesting to see what happens if we cut
out many of these plane figures of the same shape and size from cardboard sheet and
stack them up in a vertical pile. By this process, we shall obtain some solid figures
(briefly called solids) such as a cuboid, a cylinder, etc. In the earlier classes, you have
also learnt to find the surface areas and volumes of cuboids, cubes and cylinders. We
shall now learn to find the surface areas and volumes of cuboids and cylinders in
details and extend this study to some other solids such as cones and spheres.
13.2 Surface Area of a Cuboid and a Cube
Have you looked at a bundle of many sheets of paper? How does it look? Does it look
like what you see in Fig. 13.1?
Fig. 13.1
That makes up a cuboid. How much of brown paper would you need, if you want
to cover this cuboid? Let us see: