DC Current through an Inductor:

Inductors will store energy in the form of a magnetic field. A Circuit holding inductors will behave differently from an easy resistance circuit. Within circuits with elements which store energy, it is general for current and voltage to exhibit exponential increase and decay shown in the Figure.

Figure: DC Current through an Inductor

The relationship among values of current reached and the time it takes to reach them is known as a time constant.  A time constant for an inductor is declared as the time needed for the current either to increase to 63.2 % of its maximum value or to decrease through 63.2 % of its maximum value that was display in the Figure.