The standard annulus:

An annulus sector:

Differently styled annuli:

Get the Area of an annulus:

The area of an annulus slice:

Plot a function over an annulus:

A capacitor is fundamentally a pair of conducting plates with an insulator between them. The capacitor's capacitance is a function of the plates' separation and the area of overlap, which allow for the creation of variable capacitors that are made of a set of half annuli that can be rotated to change the overlap between them. Make a function that returns the arc of overlap for two concentric annuli:

Then make a function that finds the area of overlap:

Knowing that , make a function that calculates the capacitance:

Create an interactive and graphical representation of a variable capacitor that displays its capacitance (in picofarads):

As a tree grows, its cross section gains growth rings of various widths, depending on the year's climate. You can use annuli to create a pattern similar to growth rings. First, generate a list of random but adjacent inner and outer radii:

Create a table of concentric annuli with a random (brownish) color:

Finally, visualize all of the annuli, along with a disk with the radius equal to the inner radius of the smallest annulus for the core:

Under certain conditions, an annular solar eclipse may occur. The term annular comes from annulus, since the relative sizes of the Sun and Moon in the sky are such that part of the Sun (the corona) is visible around the Moon, forming a bright annulus. One can make an interactive demonstration of this phenomenon, and make a bright white annulus appear at the moment of annular eclipse:

A Disk is the limit of Annulus as goes to 0:

A Circle is the limit of Annulus as goes to :

An annulus is the closure of RegionDifference between two concentric Disk regions:

ImplicitRegion can represent any Annulus:

ParametricRegion can represent an Annulus:

Annulus is the points less than from a circle with radius :

Random annulus collections:

A family of annuli:

Digital petals: