Below is a diagram of a cylinder. Notice that it has two parallel congruent circular bases. The curved face of the cylinder is one large rectangle. The length of the rectangle will equal the circumference of the circle. The height of the rectangle will equal the original height of the cylinder.
In fact, if you were to ‘unwrap’ a cylinder, here is what you would see: r r h h r r 2πr r
h
Worked example 1
(i) Calculate the circumference of the top face of the cylinder to the nearest whole number.
(ii) Draw the net of the cylinder shown.
Solution (i)
4 cm r
h 8 cm
Remember: when no value is given for π, you can use the π button on your calculator.
(ii)
r 4 cm 25 cm h = 8 cm
Finding the surface area of a cylinder The three formulae we use to fi nd the surface area of cylinders are as follows:
radius radius radius
height
height
height
Hollow cylinder (no top or bottom) Curved surface area (CSA) = 2 × π × radius × height
CSA = 2πrh 68 Linking Thinking 2
Open cylinder (no top, but has a base) Total surface area (TSA) = 2 × π × radius × height