Chapter 13 Class 9 Surface Areas and Volumes

Class 9
Important Questions for Exam - Class 9

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Ex 11.2, 9 Assume π = 22/7, unless stated otherwise. A right circular cylinder just encloses a sphere of radius r . Find surface area of the sphere, Radius of sphere = r Surface Area of sphere = 4πr2 Ex 11.2, 9 Assume π = 22/7, unless stated otherwise. A right circular cylinder just encloses a sphere of radius r . Find (ii) curved surface area of the cylinder, Curved Surface area of cylinder = 2𝜋rh Radius of cylinder = r It can be seen that Height of cylinder is twice the radius Height of cylinder (h)= r + r = 2r Curved Surface area of cylinder = 2𝜋rh = 2𝜋r(2r) = 4𝜋r2 Ex 11.2, 9 Assume π = 22/7, unless stated otherwise. A right circular cylinder just encloses a sphere of radius r . Find (iii) ratio of the areas obtained in (i) and (ii). Ratio = (𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑠𝑝ℎ𝑒𝑟𝑒 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑖𝑛 (𝑖))/(𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑖𝑛 (𝑖𝑖)) = (4𝜋𝑟^2)/(4𝜋𝑟^2 ) = 1/1 So the ratio is 1 : 1