# Circle Properties 2

A circle is a plane figure bounded by one curved line, every point of which is equally distant from a certain point within, which is called its center. Definitions related to circles:

Arc:Â  A continuous piece of a circle is called an arc. In other words, any portion of the circumference of a circle is called an arc.

Chord: A straight line joining any two points on the circumference of a circle is called a chord.

Circumference: The perimeter of a circle is called its circumference

Diameter:Â  Any straight line drawn through the centre and terminating at both ways by the circumference is called a diameter.

Origin:Â  Origin refers to the center of a circle

Pi ( Â ):Â  An approximate value of Â is 22/7 which is correct to two decimal places. A more accurate value of Â is 3.14159 which is correct to five decimal places. Â

Radius: The constant distance of every point on the circle from its centre is called the radius of the circle. It is half of the diameter.

Sector:Â  A sector is that part of a circle, which lies between an arc and two radii joining the extremities of the centre. The most important sector is a quadrant, which is one-fourth of the circle. Â

Tangent of a circle:Â  It is a line perpendicular to the radius that touches only one point on the circle.

Circumference of a circle: = 2 r where Â is 22/7 or 3.14159

Area of a circle = r2

Length of a Circular Arc: (with central angle )

• if the angle Â is in degrees, then length = Â x ( /180) x r
• if the angle Â is in radians, then length = r x Area of Circle Sector: (with central angle )

• if the angle is in degrees, then area = ( /360) x Â r2
• if the angle is in radians, then area = [( /(2 )] x r2

If you feel you’re ready, try the circle test.