In which circuit type does the current flow instantly when energized?

The purely resistive DC circuit allows current to flow instantly when energized because of its straightforward nature. In a resistive circuit, the resistance (which opposes the flow of current) is the only factor present, and there are no components like inductors or capacitors that would delay the current flow. When voltage is applied across a resistor in this type of circuit, the current will respond immediately, following Ohm's Law (V = IR), where the voltage (V) applied leads to an instantaneous current proportional to that voltage divided by the resistance (R).

In contrast, inductive and capacitive circuits introduce elements that affect current flow differently. An inductive circuit will have components that oppose changes in current flow, introducing a delay due to the inductor creating back electromotive force (back EMF). A capacitive circuit stores energy temporarily as electric charge, which can also lead to a delay before a current steady state is reached once it is energized. AC circuits fluctuate in current direction and often require a period of time to stabilize, whereas the purely resistive DC circuit provides immediate current flow without any such complexities.