Lesson Note for Mathematics, Third (3rd) Term (Week 5) | NUE, NAPPS Scheme
Circle
Mathematics – Grade 5
Week 5: Topic – Circle
A circle is a round, curved shape where all points are the same distance from a fixed point called the center.
(a) Identifying Parts of a Circle
1. Radius:
The radius is the distance from the center of the circle to any point on the circle. A circle has many radii, but all are the same length.
2. Diameter:
The diameter is the distance across the circle, passing through the center. It is twice the radius.
Formula: Diameter = 2 × Radius
3. Circumference:
The circumference is the distance around the circle (its boundary).
Formula: Circumference = π × Diameter or π × 2 × Radius, where π (pi) = 3.14
(b) Circles with Different Radii, Diameters, and Circumferences
A circle can be small or big depending on the radius. The larger the radius, the larger the diameter and circumference.
Example:
– Radius: 4 cm → Diameter: 8 cm → Circumference: ≈ 25.12 cm
– Radius: 7 cm → Diameter: 14 cm → Circumference: ≈ 43.96 cm
(c) Identifying and Determining Radius or Diameter from Circumference
To find the radius from the diameter:
Radius = Diameter ÷ 2
To find the diameter from the radius:
Diameter = 2 × Radius
To find the radius from circumference:
Radius = Circumference ÷ (2 × π)
To find the diameter from circumference:
Diameter = Circumference ÷ π
(d) Relationship Between Radius and Diameter
The radius is half of the diameter: r = d ÷ 2
The diameter is twice the radius: d = 2 × r
(e) Quantitative Aptitude on Circle
Examples:
1. Radius = 6 cm → Diameter = 12 cm
2. Radius = 7 cm → Circumference = 43.96 cm
3. Diameter = 16 cm → Radius = 8 cm
4. Circumference = 31.4 cm → Diameter = 10 cm
Circle Diagrams
Instructional Materials
– Cardboard paper with circles
– Mathematical sets
– String or thread to measure circumference
– Ruler or tape
– Charts showing labelled parts of a circle
Class Fun (Class Work)
1. Draw a circle and label the radius, diameter, and circumference.
2. Find the circumference of a circle with radius 5 cm.
3. A circle has a diameter of 18 cm. What is its radius?
4. If the circumference of a circle is 62.8 cm, find the diameter.
5. Draw two circles with different radii. Measure and label the diameter and radius.
Home Fun (Home Work)
1. Measure the diameter of a plate at home using a ruler. Find its radius.
2. A circle has radius 9 cm. Calculate its circumference.
3. Draw a circle with a radius of 4 cm.
4. If the circumference of a circle is 37.68 cm, what is its radius?
Conclusion
A circle is an important shape in mathematics. It has parts like radius, diameter, and circumference. The radius is half the diameter, and the circumference is the round length of the circle. Understanding these parts helps us to measure and solve problems involving circles.
Reference
– New Method Mathematics Book 5
– Universal Basic Education Curriculum for Mathematics
– Mathematics for Primary Schools by MAN
– Teacher’s Guide on Quantitative Reasoning