Question

Difficulty: HardCapacitors

An electronics technician is repairing a power supply filter network. The circuit requires replacing a section containing two 12 μF12\text{ }\mu\text{F} capacitors connected in series, which are arranged in parallel with a single 6 μF6\text{ }\mu\text{F} capacitor. What is the total equivalent capacitance of this entire combination?

  1. A
    4.8 μF4.8\text{ }\mu\text{F}
  2. 12 μF12\text{ }\mu\text{F}Answer
  3. C
    30 μF30\text{ }\mu\text{F}
  4. D
    12 nF12\text{ nF}

Answer

The total equivalent capacitance of the network is 12 μF12\text{ }\mu\text{F}.
To find the total equivalent capacitance, solve the series combination first: two 12 μF12\text{ }\mu\text{F} capacitors in series provide an equivalent capacitance of 12×1212+12=6 μF\frac{12 \times 12}{12 + 12} = 6\text{ }\mu\text{F}. Next, add the parallel branch value directly: 6 μF+6 μF=12 μF6\text{ }\mu\text{F} + 6\text{ }\mu\text{F} = 12\text{ }\mu\text{F}.

Step-by-Step Solution

1
Calculate the equivalent capacitance of the two series-connected capacitors.
Cseries=6 μFC_{\text{series}} = 6\text{ }\mu\text{F}
Capacitors in series combine reciprocally using the formula Cseries=C1×C2C1+C2=12×1212+12=14424=6 μFC_{\text{series}} = \frac{C_1 \times C_2}{C_1 + C_2} = \frac{12 \times 12}{12 + 12} = \frac{144}{24} = 6\text{ }\mu\text{F}.
2
Add the equivalent series capacitance to the parallel capacitor.
Ctotal=12 μFC_{\text{total}} = 12\text{ }\mu\text{F}
Capacitors in parallel add directly together: Ctotal=Cseries+C3=6 μF+6 μF=12 μFC_{\text{total}} = C_{\text{series}} + C_3 = 6\text{ }\mu\text{F} + 6\text{ }\mu\text{F} = 12\text{ }\mu\text{F}.

Key Concept

Capacitors in series combine reciprocally (reducing total capacitance), whereas capacitors in parallel add directly together (increasing total capacitance).

Alternative Method

Since the two series capacitors are identical, their equivalent capacitance is simply half of one capacitor's value: 12 μF2=6 μF\frac{12\text{ }\mu\text{F}}{2} = 6\text{ }\mu\text{F}. Adding the identical 6 μF6\text{ }\mu\text{F} parallel branch doubles this value back to 12 μF12\text{ }\mu\text{F}.
Estimated Time:1m 30s
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