FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsMedium
A capacitor with a capacitance of 10 microfarads is connected to a 1,000 Hz AC source. What is the capacitive reactance of this capacitor?
- A15.9 ohms
- B1,590 ohms
- C1.59 ohms
- D159 ohms
Show answer & explanationAnswer & explanation
Correct answer: A. 15.9 ohms
Capacitive reactance is Xc = 1/(2πfC). Substituting: Xc = 1/(2 × 3.14 × 1000 × 0.00001) = 1/0.0628 ≈ 15.9 ohms.
Why the other options are wrong
- B. This value is off by a factor of 100 from the correct answer.
- C. This is off by a factor of ten from the correct calculation.
- D. This is ten times too large, likely a decimal placement error.
Capacitive Reactance (Xc)
The opposition a capacitor presents to AC current flow, which decreases as frequency or capacitance increases.
- Formula: Xc = 1/(2πfC)
- Inversely proportional to frequency and capacitance
- Measured in ohms
Memory trick: Capacitors 'open up' to higher frequencies — Xc shrinks as f and C grow.