USCG Exam PracticeDC circuits and electronic principles
Two capacitors, 20 µF and 5 µF, are connected in series across a DC supply. Which of the following correctly describes the total capacitance?
- A. 25 µF, because capacitors in series add directly.
- ✓ 4 µF, because the reciprocal rule gives a total less than the smallest capacitor.Correct
- C. 10 µF, because the product-over-sum rule applies as it does for parallel resistors.
- D. 2.5 µF, because series connection halves the capacitance of the larger capacitor.
Why B is correct
Capacitors in series combine by the reciprocal rule: 1/Ct = 1/20 + 1/5 = 0.05 + 0.20 = 0.25, so Ct = 4 µF. The result is always less than the smallest individual capacitance. Direct addition applies to capacitors in parallel, not series. (NEETS Mod. 2 §3-2)
Cited:NEETS Mod. 2 §3-2