Introduction: Chapter 22 Surface Area and Volume of a Right Circular Cylinder RD Sharma Class 8 Math
Channel: Math Solutions Foundation
Date: 17/01/2021

In this video, the following topics have been discussed:
(i) Right Circular Cylinder
(ii) Definitions of some basic terms : Base, Axis, Radius, Height, etc.
(iii) Surface Area of a Right Circular Cylinder 
(iv) Surface Area of Hollow cylinder 
You can watch this video for the following details:
In our day to day life, we come across several solids like measuring jars, circular pillars, circular pipes, a garden roller, gas cylinder etc. These solids have a curved (lateral) surfaces with congruent circular ends. Such solids are right circular cylinders. 
A right circular cylinders has two plane ends. Each plane end is circular in shape, and the two plane ends are parallel; that is, they lie in parallel plane. Each of the plane end is called a base of the cylinder.
Axis : The line segment joining the centres of two bases is called the axis of the cylinder. 
We observe that in a right circular cylinder both circular faces are parallel and congruent and curved surface is perpendicular to them.
An alternative definition  A solid generated by the revolution of a rectangle about one of its sides is called a right circular cylinder. 
Remark 1: If the line joining the centres of circular ends of a cylinder is not perpendicular to the circular ends, then the cylinder is not a right circular cylinder. 
Remark 2: If we take a number of circular sheets and stake them up vertically, we get a right circular cylinder.
In case circular sheets are not stacked up vertically then the cylinder is not a right circular cylinder. However, it is a circular cylinder but not a right circular cylinder.
If the base is not circular then, the cylinder with a non-circular base is a right cylinder but not a circular one.
Note: From now onwards, in this chapter, the word 'cylinder' will always mean the right circular cylinder.
Definitions of some terms:
As discussed earlier that a right circular cylinder has two plane ends. Each plane end is circular in shape, and the two plane ends are parallel. 
Base: Each of the circular ends on which the cylinder rests is called its base.
Axis: The line segment joining the centres of two circular bases is called the axis of the cylinder. 
Radius: The radius of the circular bases is called the radius of the cylinder.
Height: The length of the axis of the cylinder is called the height of the cylinder
In other words, the perpendicular distance between the two parallel plane ends or the altitude to either base from a point on the other is called the height of the cylinder.
Lateral Surface: The curved surface joining the two bases of a right circular cylinder is called its lateral surface.
Surface Area of a Right circular cylinder class 8
Surface Area of a hollow right circular cylinder class 8