We will take a right circular cone and remove a portion of it. There are so many ways in which we can do this.
But one particular case that we are interested in is the removal of a smaller right circular cone by cutting the given cone by a plane parallel to its base. You must have observed that the glasses (tumblers), in general, used for drinking water, are of this shape. (See Fig. 13.19)
`text ( Activity 1 : )` Take some clay, or any other such material (like plasticine, etc.) and form a cone. Cut it with a knife parallel to its base.
Remove the smaller cone. What are you left with?You are left with a solid called a frustum of the cone. You can see that this has two circular ends with different radii.
So, given a cone, when we slice (or cut) through it with a plane parallel to its base (see Fig. 13.20) and remove the cone that is formed on one side of that plane, the part that is now left over on the other side of the plane is called a frustum* of the cone.