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 = 2πr
where r is the radius of circle.
And π is an irrational number whose approximate value is 227 or 3.1415….. unless specified, the value of π should be taken as 227
Circumference (Perimeter) of Semicircle
Perimeter of Semicircle = πr + 2r = r(π+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
⟹ Radius = 212 = 10.5 cm
Circumference = 2πr = 2×227×10.5 = 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.
∴ Its radius, r = d2 = 142 = 7 m
∴ Perimeter of semi-circle of radius 7 m = πr + 2r = 227×7 + 2×7 = 36 m
Hence, the required perimeter is 36 m.