<Dd> L = μ 0 N 2 A l . (\ displaystyle L = \ mu _ (0) (\ frac (N ^ (2) A) (l)).) </Dd> <P> A table of inductance for short solenoids of various diameter to length ratios has been calculated by Dellinger, Whittmore, and Ould . </P> <P> This, and the inductance of more complicated shapes, can be derived from Maxwell's equations . For rigid air - core coils, inductance is a function of coil geometry and number of turns, and is independent of current . </P> <P> Similar analysis applies to a solenoid with a magnetic core, but only if the length of the coil is much greater than the product of the relative permeability of the magnetic core and the diameter . That limits the simple analysis to low - permeability cores, or extremely long thin solenoids . The presence of a core can be taken into account in the above equations by replacing the magnetic constant μ with μ or μ μ, where μ represents permeability and μ relative permeability . Note that since the permeability of ferromagnetic materials changes with applied magnetic flux, the inductance of a coil with a ferromagnetic core will generally vary with current . </P>

Where do you make use of a solenoid