Formula for Circumference of Circle (Perimeter) – Examples

Here you will learn what is the formula for circumference of circle (perimeter of circle) with examples.

Let’s begin –

What is Circumference ?

The perimeter (boundary) of a circle is called its circumference. It is the distance covered by travelling once around circle.

Formula for Circumference of Circle (Perimeter of Circle)

Circumference of circle = \(2\pi r\) 

where r is the radius of circle.circumference of circle

And \(\pi\) is an irrational number whose approximate value is \(22\over 7\) or 3.1415….. unless specified, the value of \(\pi\) should be taken as \(22\over 7\)

Circumference (Perimeter) of Semicircle

Perimeter of Semicircle = \(\pi r\) + 2r = \(r(\pi + 2)\)

Rotating Wheels

(i) Distance moved by a wheel in 1 rotation = circumference of the wheel

(ii) Number of rotations in 1 minute = distance moved in 1 minute/circumference.

Example : Find the circumference of the wheel of cycle’s whose diameter is 21 cm.

Solution : We have, Diameter = 21 cm 

\(\implies\)   Radius = \(21\over 2\)  = 10.5 cm

Circumference = \(2\pi r\)  = \(2 \times {22\over 7} \times 10.5\) = 66 cm

Hence, the circumference of wheel of cycle is 66 cm

Example : If the diameter of a semi-circular plot is 14 m, then find its perimeter.

Solution : A semi-circle has been drawn with AB = 14 m as diameter.

\(\therefore\)  Its radius,     r = \(d\over 2\) = \(14\over 2\) = 7 m

\(\therefore\)   Perimeter of semi-circle of radius 7 m = \(\pi r\) + 2r  = \({22\over 7} \times 7\) + \(2\times 7\) = 36 m

Hence, the required perimeter is 36 m.

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