Final answer:
The time for one complete cycle of the aircraft's electric power supply with Avionics Ventilation system in the normal configuration is 2.5 milliseconds.
Step-by-step explanation:
In military aircraft, the electric power supply with Avionics Ventilation system in the normal configuration has a frequency of 400 Hz. To find the time for one complete cycle of this power, we need to calculate the period. The period is the reciprocal of frequency, so the period is 1/frequency. Therefore, the time for one complete cycle of this power is 1/400 Hz, which is 0.0025 seconds or 2.5 milliseconds.