Loop Coil Comparison: Hollow Tubing vs. Solid Wire

[japam]

Is the same inductance formula valid for a coil made of hollow tubbing that for a solid wire made , with both having the same width?,
and supposing that a high frequency current flows through it
whats the skin effect influence on the result

 

[berkeman]

Is this homework? What is the application? What are the physical dimensions, and what is the frequency range of interest?