FOR GMS ICSE 2014 6TH SEPT

Ch 22 : Surface Area and Volume (continued)

Before we proceed we need to revise the formulas we have learnt. Can you remember the following formulas :

• Volume of a cylinder ?
• Curved surface area of a cylinder ?
• Total Surface area of a cylinder ?
• Volume of the metal (or material) of an open cylinder ?
• curved surface area of a cone ?
• total surface area of a cone ?
• volume of a cone ?

Now that you have revised those, please remember that we need to regularly revise these and other formulas we need to keep in mind - just trying t study them before an exam or test will mix things up in our heads !!!

Let us now move ahead to a Sphere ! A basketball is a sphere, to is a tennis ball and a football. So what will be a hemisphere ? I'm sure that you have come across that word in Geography - in which subject it refers either to the Northern or southern half. Is the earth a sphere ? NO ! It's it's own shape !!!

There are two formulas to be learnt here :

• Surface Area of a sphere : 4πr²

• So, what will be the total surface area of a hemisphere ? It will be 3πr²  - half (curved surface) of the sphere : 2πr² and the circular section πr²

• Volume of a sphere is 4/3 πr³

• So what will be the volume of a hemisphere ? half of a sphere which is 2/3 πr³ 

So, let us try and work out the following sums : Ex 22 (C) : Nos. 1, 2, 9 and 10