Question

Difficulty: MediumCapacitors and Capacitance

Two 12 μF12\text{ }\mu\text{F} capacitors are connected in series, and this combination is placed in parallel with a third capacitor of capacitance 6 μF6\text{ }\mu\text{F}. What is the total equivalent capacitance of the arrangement?

  1. A
    3.0 μF3.0\text{ }\mu\text{F}
  2. B
    4.8 μF4.8\text{ }\mu\text{F}
  3. 12.0 μF12.0\text{ }\mu\text{F}Answer
  4. D
    30.0 μF30.0\text{ }\mu\text{F}

Answer

The total equivalent capacitance of the network is 12.0 μF12.0\text{ }\mu\text{F}.
Combining the two identical 12 μF12\text{ }\mu\text{F} capacitors in series gives an equivalent capacitance of 6.0 μF6.0\text{ }\mu\text{F}. Adding this in parallel with the 6.0 μF6.0\text{ }\mu\text{F} capacitor yields 6.0 μF+6.0 μF=12.0 μF6.0\text{ }\mu\text{F} + 6.0\text{ }\mu\text{F} = 12.0\text{ }\mu\text{F}.

Step-by-Step Solution

1
Calculate the equivalent capacitance (CsC_s) of the two 12 μF12\text{ }\mu\text{F} capacitors connected in series.
Cs=12×1212+12=6.0 μFC_s = \frac{12 \times 12}{12 + 12} = 6.0\text{ }\mu\text{F}
Capacitors in series combine reciprocally: 1Cs=1C1+1C2\frac{1}{C_s} = \frac{1}{C_1} + \frac{1}{C_2}.
2
Calculate the total equivalent capacitance (CeqC_{eq}) by adding CsC_s to the parallel 6.0 μF6.0\text{ }\mu\text{F} capacitor.
Ceq=Cs+C3=6.0 μF+6.0 μF=12.0 μFC_{eq} = C_s + C_3 = 6.0\text{ }\mu\text{F} + 6.0\text{ }\mu\text{F} = 12.0\text{ }\mu\text{F}
Capacitors in parallel add directly: Ceq=Cseries+CparallelC_{eq} = C_{series} + C_{parallel}.

Key Concept

Equivalent capacitance of series-parallel capacitor networks
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