FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsHard
A resistor-capacitor (RC) circuit consists of a 100,000-ohm resistor and a 10-microfarad capacitor connected in series to a DC source. How long does it take for the capacitor to reach approximately 63.2 percent of the applied voltage?
- A1 second
- B0.1 second
- C100 seconds
- D10 seconds
Show answer & explanationAnswer & explanation
Correct answer: A. 1 second
The RC time constant is calculated as T = R × C = 100,000Ω × 0.00001F = 1 second, which is the time for the capacitor to charge to 63.2% of the applied voltage.
Why the other options are wrong
- B. This would result from an incorrect decimal placement in the calculation.
- C. This overstates the time constant by a factor of 100.
- D. This overstates the time constant by a factor of 10.
RC Time Constant
The time constant (T=RC) determines how quickly a capacitor charges or discharges through a resistor in a series circuit.
- One time constant = 63.2% of full charge
- Capacitor is considered fully charged after about 5 time constants
- T=R×C, measured in seconds
- Larger R or C values result in slower charging
Memory trick: RC is like filling a bathtub — bigger resistance/capacitance means slower fill.