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Circumference and area of a circle
Dynamic tasks on radius, diameter, circumference and the area of a circle and its parts, using π ≈ 3.14.
Questions: 10Estimated time: 19 minutes
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Question 1out of 10
A wheel has radius 6 cm. How far does it travel in 12 complete revolutions? Use π ≈ 3.14.
In one complete revolution without slipping, a wheel travels its circumference, 2 × π × r. For n revolutions, distance = n × 2 × π × r. Use π ≈ 3.14.
Question 2out of 10
A semicircle has radius 14 cm. Calculate the area of the semicircle using π ≈ 3.14.
A semicircle area is half the full circle area: S = π × r² ÷ 2. Use π ≈ 3.14. Express the result in cm².
Question 3out of 10
The radius of a circle is 2 cm. Calculate its area using π ≈ 3.14.
Circle area is S = π × r². Multiply the radius by itself, then by 3.14. Use cm².
Question 4out of 10
The radius is 12 cm. Calculate the circumference using π ≈ 3.14.
Circumference is C = 2 × π × r. Use 3.14 for π and multiply by twice the radius. This is a length in centimetres, not an area.
Question 5out of 10
If a circle’s radius is multiplied by 3, by what factor does its area increase?
Area depends on the radius squared: S = πr². Multiplying the radius by k multiplies the area by k². For example, doubling the radius quadruples the area.
Question 6out of 10
The radius of a circle is 5 cm. Calculate its area using π ≈ 3.14.
Circle area is S = π × r². Multiply the radius by itself, then by 3.14. Use cm².
Question 7out of 10
The radius of a circle is 15 cm. Find its diameter.
The diameter passes through the centre and consists of two radii. Therefore d = 2 × r.
Question 8out of 10
Which statement correctly explains the difference between a circle and a disk?
The circumference is the boundary of a circle and is measured in length units. The disk includes the interior as well as its boundary; its area is measured in square units.
Question 9out of 10
If a circle’s radius is multiplied by 4, by what factor does its area increase?
Area depends on the radius squared: S = πr². Multiplying the radius by k multiplies the area by k². For example, doubling the radius quadruples the area.
Question 10out of 10
A quarter-circle has radius 18 cm. Calculate only the arc length using π ≈ 3.14.
A quarter-circle arc is one quarter of the circumference: l = 2 × π × r ÷ 4. Only the arc is requested, so do not add the lengths of the two radii.
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Sample questions
- The radius of a circle is ___ cm. Find its diameter.
- The radius is ___ cm. Calculate the circumference using π ≈ 3.14.
- The radius of a circle is ___ cm. Calculate its area using π ≈ 3.14.
- A semicircle has radius ___ cm. Calculate the area of the semicircle using π ≈ 3.14.
- A quarter-circle has radius ___ cm. Calculate only the arc length using π ≈ 3.14.
Circumference and area of a circle
The circumference is the boundary of a circular region. Radius r joins the centre to the boundary, while diameter d = 2r passes through the centre. Circumference C = 2πr = πd and area A = πr².
Parts of a circle
Divide the full area by 2 or 4 for a half or quarter. Use the stated value of π. Circumference uses units of length, while area uses square units.
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