Final answer:
A cylinder with inner radius a and outer radius na is a cylindrical annulus or hollow cylinder with the outer radius being n times larger than the inner. It is used in various engineering and physics applications, such as cylindrical capacitors or coaxial cables, where the ratio of the radii is significant.
Step-by-step explanation:
The description of a cylinder with inner radius a and outer radius na likely refers to a cylindrical annulus or a hollow cylinder. This geometric figure can be visualized as a solid cylinder with another concentric cylinder removed from it, where the removed cylinder has a radius a, and the remaining outer shell extends to a radius of na. The value of n represents a scalar multiplier indicating how many times larger the outer radius is than the inner radius.
Applications of this concept can be found in the engineering of cylindrical capacitors or physical systems involving concentric cylinders such as coaxial cables, where the ratio of radii can affect the capacitance or other physical properties. In physics, such hollow cylinders are analyzed for their moment of inertia or in electrodynamics for magnetic fields and charge distributions.