This is a problem made by my professor.
Imagine having to repair a radio in a rural area, without any high-tech instruments, and I need to build a solenoid with an inductance of 100uH, a cross-section area of 1.00 cm2 and a lenght of 3.00cm.
Do I need to find the number of turns and their diameter, explaining also the type of material I would use?
I found some formulas, such as L = [d2 n2] / [18d + 40l] , or this L = u0 * (n2/l) * S . What's the difference between them?
https://www.electricaltechnology.org/2014/03/inductance-air-core-inductor-calculator.html (This is the link to the first formula, while the second one was found in my physics' course book).
I know that I have to find the number of turns and their diameter, the only thing I don't know is which formula do I have to use.