Circles · Grade 6
In Circles (Grade 6) you practise 3 skills: Centre, radius, diameter and chord · The circumference of a circle · The area of a disc. A circle is a round closed line, and every point on it is the same distance from the centre. The disc is the whole region the circle closes in. A radius is a segment from the centre to the circle. A chord joins two points on the circle, and a diameter is the chord through the centre. The diameter is twice as long as the radius, and it is the longest chord.
Roll a circle one full turn and it travels a little more than three diameters. The exact number is called pi, and it is about 3.14. So the circumference of a circle is about 3.14 times the diameter. The area of a disc is more than 3 times the radius times the radius, but less than 4 times. It is about 3.14 times the radius times the radius. When the radius is twice as long, the circumference is twice as big, but the area is four times as big. The third level has a challenge, too: the area of a ring between two circles.
Tip: When you are given the radius, double it to get the diameter before you work out the circumference.
What you learn
Centre, radius, diameter and chord
For example: What is drawn here, a circle or a disc?
- A disc
- A circle
Answer and solution
The answer: A disc
The whole region inside the line is shaded, so this is a disc.
The circumference of a circle
For example: The diameter of the circle is 10 cm. What is its circumference? Use π ≈ 3.14
Answer and solution
The answer: 31.4 cm
The circumference of a circle is π times the diameter, about 3.14 times the diameter: 3.14 × 10 = 31.4
The area of a disc
For example: The radius of the disc is 10 cm. What is the area of the disc? Use π ≈ 3.14
Answer and solution
The answer: 314 cm²
The area of a disc is π times the radius times the radius: 10 × 10 = 100 Multiply by 3.14: 3.14 × 100 = 314
Not on the site yet
Parts of this topic that are not built yet: Naming a sector and an arc · Polygons and circles.
The exercises are made by rules and the answers are worked out in code, so there are new exercises every time. The topic follows the new Israeli elementary programme (2023).