Friday, January 25, 2013

Surface Area of Prisms and Cylinders

Introduction about prism and cylinder:

Prism:

In geometry, an n-sided prism is a polyhedron made of an n-sided polygonal base, a translated copy, and n faces joining corresponding sides. Thus these joining faces are parallelograms

Cylinder:

A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given straight line, the axis of the cylinder.

(Source – Wikipedia)


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Formula Used to Find the Surface Area of the Prism and Cylinder:

Rectangular prism:

Surface area of the rectangular prism (A) = 2(wh + lw + lh) square units

w – Width

h – Height

l – Length

Triangular prism:

Total Surface Area of the triangular prism (T.S.A)

T.S.A = L.S.A + 2 x Base Area

Total surface area T.S.A = (P x h + 2 A) sq. units

P - Perimeter

A - Area of the base

h - Height of the prism

Cylinder:

Surface area of cylinder (SA) = 2 p r^2 + 2 p r h square units

r – Radius

h – Height

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Surface Area of Prisms and Cylinders - Example Problems:

1. The rectangular prism has the length 25 cm, width 13cm and height 10 cm. find the surface area of the rectangular prism.

Solution:

Given:

Length (l) = 25 cm

Width (w) = 13 cm

Height (h) = 10 cm

Formula to find the surface area of the rectangular prism:

Surface area (A) = 2(wh + lw + lh) square units

= 2 (13 x 10 + 25 x 13 + 25 x 10)

= 2 (130 + 325 + 250)

= 2 (705)

= 1410

Surface area of the rectangular prism (A) = 1410 cm 2

2. The triangular prism has the base side length 3 cm, 4cm and 5 cm. its height is 10 cm. find total surface area of prism.

Solution:

Given:

Three side length of triangular prism = 3 cm, 4 cm, 5 cm

Height of the prism = 10 cm

Base of the triangle = 3 cm

Height of the triangle = 4 cm

The lateral surface area of the prism = p x h square units

= (3 + 4 + 5) x 10

=12x10
L.S.A =120 cm2

Now the area of the bases, A = 1/2 bh square units

h is the height of the triangle

= 1/2 x 3 x 4

A= 6 cm2

The total surface area of the prism = p h + 2 A square units

= 120 + 2 x 6

Total surface area of the prism  =  1440 cm2

3. The cylinder has radius r = 3 cm, h= 12 cm. Find the surface area of cylinder.

Solution:

Given:

r= 3 cm

h=12 cm

Geometric Formula:

The surface area of the cylinder  = 2 p r^2 + 2 p r h square units

= 2 x 3.14 x 32 + 2 x 3.14 x 3 x 12

= 56.52 + 226.08

The surface area of the cylinder = 282.6 cm2

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