Circumference of the circle is the measurement of the boundary across any two-dimensional circular shape including circle. The concept of the perimeter of a circle is covered here along with its definition, formula and method to know the same by using formula and physical method along with some solved examples. Finding area of a circle also requires the same radius as for finding the circumference.
What is the Circumference of Circle?
The circumference is the distance around a circle or any curved geometrical shape. It is the one-dimensional linear measurement of the boundary across any two-dimensional circular surface. It follows the same principle behind finding the perimeter of any polygon which is why calculating the circumference of a circle which is also known as the perimeter of a circle.
A circle is defined as a shape with all the points are equidistant from a point at the centre. The circle depicted below has its centre lies at point A.
The value of pi is approximately 3.1415926535897… and we use a Greek letter π (pronounced as Pi) to describe this number. The value π is a non-terminating value.
For circle A (as given above), the circumference and the diameter will be-
In other words, the distance surrounding a circle is known as the circumference of the circle. The diameter is the distance across a circle through the centre and it touches the two points of the circle perimeter. π shows the ratio of the perimeter of a circle to the diameter. Therefore, when you divide the circumference by the diameter for any circle, you obtain a value close enough to π. This relationship can be explained by the formula mentioned below.
C/d = π
Where C indicates circumference and d indicates diameter. A different way to put up this formula is C = π × d. This formula is mostly used when the diameter is mentioned and the perimeter of a circle needs to be calculated.
Circumference Formula of a Circle
The Circumference (or) perimeter of a circle = 2πR
R is the radius of the circle
π is the mathematical constant with an approximate (up to two decimal points) value of 3.14
Pi (π) is a special mathematical constant, it is the ratio of circumference to diameter of any circle.
where C = π D
C is the circumference of the circle
D is the diameter of the circle
Area of a Circle
Area of any circle is the region enclosed by the circle itself or the space covered by the circle. The formula to find the area of the circle is;
A = πr2
Where r is the radius of the circle. This formula is applicable to all the circles with different radii.
Radius of a Circle
The distance from the centre to the outer line of the circle is called a radius. It is the most important quantity of the circle based on which formulas for area and circumference of the circle are derived. Twice the radius of a circle is called as the diameter of the circle. The diameter cuts the circle into two equal parts, which is called as a semi-circle.
Methods to Calculate the Circumference of a Circle
Method 1: Since it is a curved surface, we can’t physically measure the length of a circle using a scale or ruler. But this can be done for polygons like squares, triangles and rectangles. Instead, we can measure the circumference of a circle using a thread. Trace the path of the circle using the thread and mark the points on the thread. This length can be measured using a normal ruler.
Method 2: An accurate way of knowing the circumference of a circle is to calculate it. For this, the radius of the circle has to be known. The radius of a circle is the distance from the centre of the circle and any point on the circle itself. The figure below shows a circle with radius R and centre O. The diameter is twice the radius of the circle.
Perimeter of a Circle Example Problems
What is the circumference of the circle with diameter 4 cm?
Since the diameter is known to us, we can calculate the radius of the circle,
Therefore, Circumference of the Circle = 2 x 3.14 x 2 = 12.56 cm.
Question 2: Find the radius of the circle having C = 50 cm.
Circumference = 50 cm
As per formula, C = 2 π r
This implies, 50 = 2 π r
50/2 = 2 π r/2
25 = π r
or r = 25/π
Therefore, the radius of the circle is 25/π cm.
Circumference of a Circle Questions
- Calculate the perimeter of a circle whose diameter is 8 cm.
- What will be the diameter of a circle if its C = 10 cm?
- If C = 12 cm, what will be its radius?
- What is the circumference of a 16-inch circle?
- What is the circumference of a 6 mm circle?
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