How can the current and voltage in A.C. circuit be controlled?

Given, 

Inductance (l) = 15 mH

Frequency (f) = 80 KH

we have; 

Inductive Reactance = 2 pi.f.L 

                                       = 2 x 3.14 x 80 x 10 ³ x 15 x 10 ^-6 

                                        = 7.536 ohm 

The A.C. ammeter works on the heating effect of the electric current. The heat produced by the electric current is directly proportional to the square of the current. Hence the divisions marked on the scale of our AC ammeter are not equally spaced. In order to have equally spaced scales, the variation should be linear or heat should be directly proportional to current, which is not the case.