Definition of Annulus
Annulus is the area between the two concentric circles having different radii.
More About Annulus
- A ring-shaped object is called as 'annulus' in Latin.
- Area (A) between two concentric circles with outer radius R and inner radius r is given by, A = Π(R2 - r2).
Examples of Annulus
Two concentric circles with outer radius R and inner radius r are shown in the figure. The region shaded with green color is annulus.
Video Examples: Area of an Annulus
Solved Example Clockple on Annulus
Ques: Find the area enclosed between the two concentric circles of radii 8 cm and 10 cm.
Choices:A. 38Π square cm
B. 37Π square cm
C. 36Π square cm
D. 40Π square cm
Correct Answer: C
Step 1: Required Area = Area of outer circle - Area of inner circle
Step 2: Required Area = Π(10)2 - Π(8)2 [Use circle area formula and substitute.]
Step 3: Required Area = Π(100 - 64) = 36Π square cm [Simplify.]