Page 184 - Maths Class 05

to construct them. A picture of the protractor is
A
given alongside.
80 100
70 90 110
A protractor has two scales – an outer scale and 60 110 100 80 70 120
50 120 60 130
inner scale. Each scale begins with 0° and ends at 40 130 50 140
30 140 40 150
180°. There are 180 equal small divisions, each 20 150 30 160
160 20
division denotes 1° (one degree). The line segment 10 170 60° 10 170
0 180 0 180 C
joining 0° and 180° is called the base line. The B
mid-point of the base line is called centre of the
protractor. An angle ABC, is given and you are Ð
A
asked to measure it using a protractor.
80 100
70 90 110
Steps for Measuring ÐABC with a Protractor 60 110 100 80 70 120
50 120 60 130
40 130 50 140
Step 1 : Place the centre of the protractor on the 140 40
30 150 30 150
vertex of Ð ABC, that is B. Adjust the 20 160 20 160
10 60° 10 170
protractor so that its base line coincides 170
0 180 0 180 C
with BC. B
Step 2 : See towards which 0° marking, the arm BC points to. In our example, BC

points to the 0° marking on the inner scale.

Step 3 : Now, read the marking of the degree line that coincides with AB. Here, AB
coincides with 60° marking.

Therefore, the measure of ABC = 60° or ABC = 60°.Ð Ð

Know
Know
Know
Get to
Get
Get
to
For measuring any angle, see towards
which 0° marking the base line points to.
If the base line points to 0° marking at the If the base line points to 0° marking at the
right side, read the inner scale. left side, read the outer scale.

80 100 80
70 90 110 A A 70 90 100 110
60 110 100 80 70 120 60 100 80 120
50 120 60 130 50 120 110 70 60 130
40 130 50 140 40 130 50 140
140 40 140 40
30 150 30 150
150 30 150 30
20 160 20 160
160 20 160 20
10 170 45° 10 170 10 170 45° 10 170
180 0 180 C
0 C 0 180 0 180
B B

Mathematics-5 184