Sky-High Success: Ace the FAA AMT Airframe Practice Exam 2025 – Soar to New Heights!

The voltage drop method of checking circuit resistance requires the input voltage to be maintained at a constant value. This is because in this method, the resistance of the circuit is calculated by measuring the voltage drop across a known resistor and using Ohm’s law to determine the resistance. If the input voltage fluctuates, the voltage drop measured will also fluctuate and therefore the calculated resistance will not be accurate. Additionally, the circuit cannot be open (option A) because a closed circuit is necessary for current to flow and create the voltage drop to be measured. And the circuit resistance cannot be zero (option D) because then there would be no voltage drop to measure.