The surface area of a cylinder is the total area of the surface of the cylinder. The surface of a cylinder consists of two congruent parallel bases and the curved surface of the cylinder. The parallel bases are circles and the curved surface is also called lateral surface of a cylinder.
The total surface area of a cylinder is the sum of the lateral area (curved surface) and the areas of the two circular bases.
The lateral area of a cylinder is the product of the circumference of the base and the height of the cylinder.
Lateral area = L.A. = 2πrh or L.A. = πdh since d = 2r.
Let B be the area of one base. The areas of the bases = 2B = πr^{2} + πr^{2} = 2πr^{2}
Total surface area of a cylinder (TSA) = S.A. = L.A. + 2B = 2πrh + 2πr^{2}
The surface area is expressed in square units.
To derive the formula of the surface area of a cylinder, we will start by showing you how you can make a cylinder. Start with the net of a cylinder consisting of a rectangle and two congruent circles.
Then, fold the rectangle until you make an open cylinder with it. An open cylinder is a cylinder that has no bases. A good real life example of an open cylinder is a pipe that is used to flow water if you have seen one before.
Next, using the two circles as bases for the cylinder, put one on top of the cylinder and put one beneath it.
Of course, the two circles will have the exact same size or the same diameter as the circles obtained by folding the rectangle.
An oblique cylinder is a cylinder whose side is not perpendicular to its base. The surface area of an oblique cylinder is still the same as the area of a right cylinder. Just make sure that the height of the cylinder is measured vertically.
S.A. = 2πrh + 2πr^{2}
The area of one base is equal to the area of outer circle - the area of inner circle.
Area of one base = πR^{2} - πr^{2} = π(R^{2} - r^{2})
Area of two bases = π(R^{2} - r^{2}) + π(R^{2} - r^{2}) = 2π(R^{2} - r^{2})
Now, we need to find the lateral area of the hollow cylinder.
Since we are dealing with two cylinders instead of one, we need to find the lateral area of two cylinders.
L.A. of the outer cylinder is 2πRh and L.A. of the inner cylinder is 2πrh.
L.A. = 2πRh + 2πrh
Total surface area of the hollow cylinder is equal to L.A. + area of two bases
Total surface area of the hollow cylinder = 2πRh + 2πrh + 2π(R^{2} - r^{2})
Total surface area of the hollow cylinder = 2πh(R + r) + 2π(R^{2} - r^{2})
Mar 29, 23 10:19 AM
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