SOLUTION

When a D.C source is switched in purely inductive, the current response is a straight line passing through the origin.

Detailed Explanation:-

Energy is stored in the electromagnetic field of an inductor when it is connected to a dc voltage source. The buildup of current through the inductor occurs in a predictable manner, which is dependent on the time constant of the circuit.

Switching of DC is an example of step excitation

The current through the inductor is given by:

$V = Lfrac{{di}}{{dt}}$

$frac{V}{L} = frac{{di}}{{dt}}$

Since V is step excitation, V/L is also step excitation

$frac{{di}}{{dt}} = step;response$

Integrating the above expression

$i = ramp;response$

Hence current through the inductor is a straight line passing through the origin.