Volume and surface area of a hollow cylinder: A solid bounded by two coaxial cylinders of same height and different radii is called a hollow cylinder.
For a hollow cylinder, whose inner radius = r, outer radius = R, perpendicular height = h.
• Curved (Lateral) surface area = External curved surface area + Internal curved surface area
= 2pRh + 2prh = 2πh (R + r) sq. units
• Area of bases = 2π (R2 – r2) sq. units
• Total surface area = 2ph (R + r) + 2p (R2 – r2)
= 2π(R + r)(h + R – r) sq. units
• Volume of material = External volume – Internal volume used in making the cylinder = πR2h – pr2h = πh(R2 – r2) cu. units
