# Chapter 20 – Volume and Surface Area of Solids – R S Aggarwal Solutions for class 8

There are two surface areas:

1) Curved surface area: It is the area of all curved region of a solid excluding the top and base area. It is also known as lateral surface area. It is also area of four walls.

2) Total surface area:  It includes the curved surface area and area of top and base of solid.

Volume: It is the total space occupied by a solid. It is measured in cubic units.

Formulas to be used in this chapter:

(1) Cuboid: It is a solid that have six rectangular plane faces.

1. Volume of Cuboid = Length × breadth × height = (l×b×h) cubic units
2. Curved surface area of cuboid = 2h (l + b) sq. units
3. Total surface area of cuboid = 2(l b + b h + h l) sq. units
4.  Diagonal of a cuboid = l2+b2+h2 units

(1I) Cube: It is a solid in which length, breadth end height are equal. It is formed by six identical or congruent squares. Let ‘a’ be the edge of cube.

(a) Volume of Cube = (edge)3=a3 cubic units

(b) Curved surface area of cube = 4 a2sq. units

(c) Total surface area of cuboid = 6a2sq. units

(d) Diagonal of a cube = 3 a units