Page 164 - Maths Class 05

Learning Objective : To understand the concept of perimeter of plane figures.

Materials Required : A book, a thread, a measuring tape / centimeter scale and pens with red
ink and blue ink.

Pre-requisite : Use of a centimeter scale for measurements.
Procedure : For (a) Measuring boundary line of the top of a book.

Step 1 : Take a book.

Step 2 : Consider its top. Place a thread at one side on
the top of the book.
D C
Step 3 : Mark a point near one end of a string with red
ink. Let this point be A.

Step 4 : Place this point of the string at one of the corner A B
of the top of the book and stretch it around the
top reaching to the same point. Put a mark again
on the string with blue ink.
Fig. 7(a)
Step 5 : Take a centimeter scale / measuring tape.
Measure the distance between the two marks.

While measuring keep the thread stretched.
Step 6 : Record the measurement as length of boundary

of the book.
For (b) Measuring boundary of a given figure. A

Step 1 : Draw a closed figure on a plane paper.

Step 2 : Mark any point A on the figure and place one
end of a thread at A and mark this end with blue
ink. [Fig. 7(b)]

Step 3 : Strech the thread along the boundary line of
figure to meet again at A. Mark this point on the
thread with red ink.

Step 4 : Measure the distance between two marks on the
thread using centimeter scale.
Fig. 7(b)
Observations :

i. The length of the boundary of the top of the book is.

ii. The length of the boundary line of the figure in Fig. 7(b) is.
Extension : Measure the boundary of different plane figures from your surroundings and
record them.

Mathematics-5 164