Perimeter of a Figure
Perimeter of a figure is explained here.
Perimeter is the total length of the boundary of a closed figure.
We know that the total length of the boundary of a plane
closed figure is called its perimeter. We can find the perimeter of a closed
figure drawn on a square sheet by adding the length of unit squares along each
side of the figure. The unit of perimeter is same as the unit of length.
The perimeter of a simple closed figure is the sum of the measures of line-segments which have surrounded the figure.
Perimeter of ∆ABC = length (AB + BC + CA)
Perimeter of the quadrilateral DEKN = length (DE + EK + KN + ND)
Perimeter of the hexagon PQRSTU = length (PQ + QR + RS + ST + TU + UP)
The perimeter of a circle is the measure of its circumference. The perimeter of the circle of center O is its circumference.
Let us draw a closed figure PQRS on a square sheet as shown below. If we make a path along its boundary starting from point P, then the total length of the path will be equal to the sum of all the sides of the figure PQRS.
Here, the length of the path is = PQ + QR + RS + SP.
We can find the length of each line segment by counting the number of unit squares. Therefore, the total length of the path = 3 + 6 + 3 + 3 = 18 unit squares.
The total length of the boundary of a plane figure is called its perimeter. The unit of perimeter is the same as the unit of length of the sides of the figure.
For example:
Find the perimeter of the following figures drawn on the 1 cm square graph sheet.
Figure (i) AB = 3 cm BC = 2 cm CD = 3 cm DA = 2 cm AB + BC + CD + DA = 3 + 2 + 3 + 2 = 10 cm Perimeter of figure 1 = 10 cm
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Figure (ii) PQ = 1 cm QR = 2 cm RS = 1 cm ST = 2 cm TU = 1 cm UV = 2 cm VW = 1 cm WP = 6 cm PQ + QR + RS + ST + TU + UV + VW + WP = 1 + 2 + 1 + 2 + 1 + 2 + 1 + 6 = 16 cm Perimeter of figure 2 = 16 cm
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Look at the given figures. Find the length of the boundary
of each of these simple closed figures made of line segments.
Length of the boundary of each figure is the sum of the
lengths of its line segments.
Length of the boundary of each figure (a) is AB + BC + CA
=
4 cm + 4 cm + 4 cm
=
12 cm
Length of the boundary of each figure (b) = 4 cm + 3 cm + 4
cm + 3 cm
=
14 cm
Length of the boundary of each figure (c) = 3 cm + 3 cm + 3
cm + 3 cm
=
12 cm
The length of the boundary of a closed figure is called the
perimeter of the figure.
1. Ken walks around a playground in his daily morning walk. How far does
he walk every morning? The playground is of the shape of a quadrilateral
having sides of length 112 m, 85 m, 69 m and 102 m.
Solution:
Perimeter of the playground
= 112 m + 85 m + 69 m + 102 m
= 368m
Ken walks 368 m around the playground, i.e. around the perimeter, every morning.
Now, answer the following questions to have a quick review
of what we have learnt so far.
1. Fill in the blanks:
(i) …………………….. is the length of the boundary of a plane
closed shape.
(ii) The perimeter of a square with side = 10 unit will be
……………………..
Answers:
(i) Perimeter
(ii) 40 units
2. Find the perimeter of the given figure if length of each
square is 1 centimetre (cm).
(i) Perimeter =
(ii) Perimeter =
(iii) Perimeter =
(iv) Perimeter =
Answers:
(i) 30 cm
(ii) 42 cm
(iii) 24 cm
(iv) 26 cm
3. Find the perimeter of the given figures.
(i)
(ii)
(iii)
(iv)
(v)
Answers:
(i) 31 cm
(ii) 26 cm
(iii) 40 cm
(iv) 28 cm
(v) 19 cm
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● Related Concepts
● Units
for Measuring Length
● Measuring
Instruments
● To
Measure the Length of a Line-segment
● Perimeter
of a Figure
● Unit of
Mass or Weight
● Examples
on Unit of Mass or Weight
● Units
for The Measurement of Capacity
● Examples
on Measurement of Capacity
● Measurement
of Time
● Read a
Watch or a Clock
● Antemeridian
(a.m.) or Postmeridian (p.m.)
● What Time it is?
● Time
in Hours and Minutes
● 24 Hour Clock
● Units of Time
● Examples
Units of Time
● Time Duration
● Calendar
● Reading
and Interpreting a Calendar
● Calendar
Guides us to Know
4th Grade Math Activities
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