Last updated at March 3, 2017 by Teachoo

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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 = (𝐼𝑛𝑛𝑒𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟)/2 = (4/2) cm = 2 cm Height (h) of cylindrical pipe = 77 cm Curved Surface Area of inner surface of pipe = 2πr1h = (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 = (𝑂𝑢𝑡𝑒𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟)/2 = (4.4/2) cm = 2.2 cm Height of cylinder = h = 77 cm Curved Surface Area of outer surface of pipe = 2πr2h = (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 𝑐𝑚, 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 = 𝜋r22 – 𝜋r12 = 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

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Davneet Singh

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