what alternating source voltage frequency is required to generate an inductive reactance of 10 in a 4mh induct

Answer 1

Hey, Mr. Un-couth is right. You have got your answer but you should know the formula also. The formula is

Inductive reactance X(L) = 2 x (pi) x f x L
where

pi = 3.14
f = frequence
L = inductance in Henry

Answer 2

10=[6.28][f][.004] f=10/[6.28][.004] f=10/.02512=398.09 Hertz This method of solving the problem is only valid if the AC voltage is a sine wave and will not work on complex wave forms