Ex 13.2, 3
A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm.
Inner curved surface area,
Inner radius of cylindrical pipe = r1 = ( )/2 = (4/2) cm = 2 cm
Height (h) of cylindrical pipe = 77 cm
Curved Surface Area of inner surface of pipe = 2 r1h
= (2 22/7 2 77) cm2
= 968 cm2
Ex 13.2, 3
A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm.
(ii) Outer curved surface area,
Outer radius of cylindrical pipe =r2 = ( )/2 = (4.4/2) cm = 2.2 cm
Height of cylinder = h = 77 cm
Curved Surface Area of outer surface of pipe = 2 r2h
= (2 22/7 2.2 77) cm2
= (2 22 2.2 11) cm2
= 1064.8 cm2
Ex 13.2, 3
A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm.
(iii) Total surface area,
r1 = 2 ,
r2 = 2.2 cm,
h = 77 cm
Total surface area = Curved Surface Area of inner cylinder
+ Curved Surface Area of outer cylinder
+ 2 Area of base
Area of base
= r22 r12
= 22/7 ((2.2)2 (2)2 )
= 22/7 (4.84 4)
= 22/7 (0.84)
= 2.74 cm2
Total surface area = Curved Surface Area of inner cylinder
+ Curved Surface Area of outer cylinder
+ 2 Area of base
= 968 + 1064.8 + 2 2.74
= 2032.8 + 5.76
= 2038.08 cm2
Therefore, the total surface area of the cylindrical pipe is 2038.08 cm2

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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