b4Circumference of a circle: This is the length of the line that marks out the circle. We can also call it perimeter of the circle.

Circumference (C) = 2 \pi r   where r = Radius of the circle.

(Note: Area of a circle = \pi r^2 )

b2A Circular Ring: This is the object that is bound by the circumference of two concentric circles of different radius.

If the radius of the outer ring is R and the radius of the inner ring is r, then the

Area of the ring = \pi (R^2 - r^2)

Semi-circle: If the circle is divided into two equal halves, then we will we will get two semi-circle.b3

Length if the arc = \pi r (half the circumference of the circle)

Perimeter of the semi-circle = \pi r + 2r

Area of the semi circle = \frac{1}{2} \pi r^2

b1Quadrant: If a circle is divided into four equal parts by two mutually perpendicular diameters,  the part so obtained is called a quadrant.

Length of the arc APC = \frac{1}{2} \pi r (one fourth of the circumference of the circle)

Perimeter of the quadrant = \frac{1}{2} \pi r + 2 r

Area of the quadrant = \frac{1}{4} \pi r^2