Key Tips for Accurate Protractor Reading and Exam Success
Protractors are useful, clear plastic tools for everyday life; we all have seen the protractor in the geometry box. They can be used for measuring different types of angles. It is a device used to measure and plot angles from 0 to 180 degrees, clockwise and anticlockwise. It has a straight edge with one or more semicircles on the edges.
The protractor has a scale usually marked with degrees or radians (any angle in minutes). It can be used for measuring angles in a plane and three-dimensional space. The protractor scale can measure angles to find the area of a triangle, the volume of a cylinder, and so on. We will be looking at a protractor scale, a scale in maths, how to read a protractor and how to use a protractor with examples in this article.
A Common Protractor
What Is a Protractor?
A protractor is a type of measuring tool that helps us find angles. It has two parts, a straightedge and a curved ruler. A line on the protractor represents the angle we are trying to find. Protractors are used in many different maths problems.
A general protractor consists of an inner and outer scale, graduated from 0 degrees to 180 degrees. It is a tool that helps us draw a line or shape using two different angles. It’s beneficial in teaching kids how to use angles and draw shapes. The tool is also helpful for artists, engineers, architects, and many more who need to measure angles. They use different kinds of protractors for accurate measurement of angles.
360-degree Protractor
A 360-degree protractor is a tool used to measure angles in a circle. It has a flat and circular surface and can be used for drawing circles. It is also used in geometry.
A 360-degree Protractor
What is Scale in Maths?
Scale in Mathematics is a range of levels or numbers used to measure numbers. Here, it is simply the angle marking from 0 degrees to 180 degrees in a general protractor.
How to Read and Use a Protractor
While measuring through a protractor, the measure is usually in degrees. If the angle is on the left side of the protractor, we use the outer edge measurement, and if the angle is on the right side of the protractor, we use the inner edge measurements.
The steps to measure and read the angle are as follows:
Step 1: Place the protractor's centre on the angle's vertex.
Step 2: Superimpose one side of the angle with the zero line of the protractor.
Step 3: The angle equals the number of degrees crossed on the protractor.
Let us look at an example to read and measure the angle of 60 degrees.
Step 1: Align the protractor with the ray OB as shown below. Start reading from the $0^{\circ}$ mark on the bottom-right of the protractor.
Reading the Protractor
Step 2: The angle measure is the number on the protractor that coincides with the second ray. Measure the angle using the number on the lower arc of the protractor.
Protractor Showing an Angle 60 Degree
Therefore, $\angle A O B=60^{\circ}$. Since the measure is greater than $0^{\circ}$ and lesser than $90^{\circ}$, we can say that $\angle A O B$ is an acute angle.
This way, we can read and use the protractor to measure the angle.
Solved Example
Q1. Find the measure of the angle given in the picture below.
Solved Example
Ans: First, place the protractor's centre perfectly on the line.
Now, look at the inner scale of the right side.
Then, check the angle passing through the line.
We get 40 degrees as the answer.
Practice Questions
Identify the angle measures.
1. The measure of the angle is _____ degrees.
Ans:
Practice Questions
Ans: 90 degrees
2. The measure of the angle is _____ degrees.
Practice Question
Ans: 135 degrees
Summary
A protractor is a measuring instrument for measuring angles, typically made of transparent plastic or glass. Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. A protractor is a great tool for measuring angles in various mathematical problems.
They are also excellent for use in geometry, measuring the slope of a line, and calculating different volumes and areas. There are two types of protractors: semi-circular (0 degrees to 180 degrees) and circular (0 degrees to 360 degrees). Engineers use these to create technical designs for different construction sites.
FAQs on How to Use a Protractor Scale: Step-by-Step Guide
1. What are the basic steps to measure an angle using a protractor?
To accurately measure an angle, follow these essential steps:
- Align the Centre: Place the central point (or hole) of the protractor directly on the vertex (the corner) of the angle.
- Set the Baseline: Line up the protractor's baseline (the 0° line) with one of the arms of the angle.
- Read the Scale: Read the measurement in degrees where the second arm of the angle crosses the protractor's scale. Ensure you are reading from the correct scale (inner or outer) that starts at 0° from your baseline arm.
2. Why does a protractor have two different scales, an inner and an outer one?
A protractor has two scales to provide flexibility when measuring angles from different orientations. One scale runs clockwise (e.g., from right to left) and the other runs counter-clockwise (from left to right). This design allows you to align the baseline on either arm of the angle and still get a correct measurement without having to turn your paper upside down. You simply choose the scale that starts at 0° on the arm you've aligned.
3. How do you draw an angle of a specific size, for example, 65 degrees?
To draw a 65° angle, follow this method:
- First, use a ruler to draw a straight line, which will be one arm of your angle. Mark a point on this line to be the vertex.
- Place the protractor's centre on the vertex and align its baseline with the line you just drew.
- Find the 65° mark on the correct scale and make a small dot on the paper.
- Finally, remove the protractor and use a ruler to draw a straight line from the vertex to the dot. This completes your 65° angle.
4. What is the most common mistake students make when using a protractor?
The most common mistake is reading from the wrong scale. After aligning the protractor's baseline with one arm of the angle, students sometimes read the number on the scale that doesn't start from zero on that baseline. Always remember to start counting from the 0° mark that lies on the first arm of the angle. Another frequent error is not placing the exact centre of the protractor on the angle's vertex.
5. How can a protractor be used to check the angles of a triangle?
You can use a protractor to measure each of the three interior angles of a triangle individually. Place the protractor on each vertex one by one and measure the angle. According to the angle sum property of a triangle, the sum of these three angles should be exactly 180°. This is a great way to check the accuracy of your measurements or your drawing.
6. What does the 'least count' of a protractor refer to?
The 'least count' of a measuring instrument is the smallest and most accurate value it can measure. For a standard school protractor, the markings are at every one degree. Therefore, the least count of a protractor is 1 degree. This means you can measure angles with an accuracy of up to one degree.
7. What are some real-world applications or uses of a protractor?
Beyond the classroom, protractors are essential tools in various fields. Key applications include:
- Architecture and Engineering: For creating precise blueprints and plans for buildings, bridges, and machines.
- Navigation: Sailors and pilots use protractors on maps to plot courses and determine bearings.
- Art and Design: Artists use them to create geometric patterns and maintain perspective in drawings.
- Carpentry: To ensure angles are cut correctly for joints and fittings.
