The dimensions of an annulus are defined by the two radii R, r, which are the radii of the outer ring and the inner ‘hole’ respectively. The area of a circular ring can be found by subtraction the area of a small circle from that of the large circle.
Here are formulas to find Area of Annulus.
A = Area of Annulus
R = Outer radius
r = Inner radius
Example : Find the area of the path, where a path is 14 cm wide, surrounds a circular lawn whose diameter is 360 cm.
Width of the path = 14 cm
Diameter of the inner circle is 360 cm.
Radius of inner circle (r) = 360/2 = 180 cm
Radius of outer circle is (R) = 180 + 14 = 194 cm
= 3.142 (R + r)(R – r)
= 3.142 (194 + 180) (194 – 180)
= 16451.512 cm2