Measure an Angle with a Protractor
Measuring an Angle
Protractor is a geometrical instrument that looks like the letter D. The angles are marked from 0° to 180° on the edge in clockwise direction as well as in anti-clockwise direction. O is the midpoint at the baseline of the protractor.
Let us measure angle ∠ABC and ∠PQR.
Place the protractor in such a way that the midpoint O of the baseline coincides with Q and the baseline exactly overlaps on line segment QR. Since QR is on the right of vertex (midpoint of base-line) O, start counting from 0° on the right side of Q and read the mark with which the arm PQ coincides. It coincides with the 40° mark. So, the measurement of ∠PQR is 40°.
Thus, ∠PQR = 40°.
Similarly to measure∠ABC, place the protractor in such a way that the midpoint O at the baseline coincides with point B and the baseline overlaps exactly on AB. Since AB is on the left of vertex O, start counting from 0° on the left side of B and read the mark with which arm BC coincides. It coincides with the 50° mark. So, the measurement of∠ABC is 50°.
Thus,∠ABC = 50°.
COMPARISON OF ANGLES
The magnitude of an angle depends upon the opening or inclination between the two rays that form the angle. If two angles have different inclination, then we say they have different magnitudes. The magnitudes of two angles can be compared in the following manner:
By observation
Observe the opening of the given angles. By the opening of two arms of the given angle, we decide which is the larger or the smaller angle.
By observing the angles, we can easily say that ∠PQR > ∠ABC.
By Measuring
We can measure the magnitude by using a protractor and then compare the two angles.
By Tracing
Trace one of the two given angles on a tracing paper and put it on top of the other angle. By doing so, we can observe which is larger or smaller.