How many turns should a solenoid of cross-sectional area 3.3×10−2 m2 and length 0.30 m have if its inductance is to be 47 mh ?

The inductance of a solenoid is given by

where
is the magnetic permittivity
N is the number of turns of the solenoid
l is its lenght
A is its cross-sectional area

By re-arranging the formula and replacing the numbers, we get the number of turns of the solenoid:

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