Question

Difficulty: EasyCapacitors and Capacitance

A 3 μF3\text{ }\mu\text{F} capacitor and a 6 μF6\text{ }\mu\text{F} capacitor are connected in series across a direct current voltage source. What is the total equivalent capacitance of the combination, in microfarads (μF\mu\text{F})?

Answer: 2 µF

Answer

The total equivalent capacitance of the combination is 2 μF2\text{ }\mu\text{F}.
For capacitors connected in series, the reciprocal of the total equivalent capacitance is equal to the sum of the reciprocals of the individual capacitances. Substituting 3 μF3\text{ }\mu\text{F} and 6 μF6\text{ }\mu\text{F} gives 1Ceq=13+16=12 μF1\frac{1}{C_{eq}} = \frac{1}{3} + \frac{1}{6} = \frac{1}{2}\text{ }\mu\text{F}^{-1}, which yields an equivalent capacitance of 2 μF2\text{ }\mu\text{F}.

Step-by-Step Solution

1
State the formula for equivalent capacitance of two capacitors in series
1Ceq=1C1+1C2\frac{1}{C_{eq}} = \frac{1}{C_1} + \frac{1}{C_2}
Capacitors connected in series combine reciprocally, unlike resistors connected in series.
2
Substitute the values of C1C_1 and C2C_2
1Ceq=13+16=36=12 μF1\frac{1}{C_{eq}} = \frac{1}{3} + \frac{1}{6} = \frac{3}{6} = \frac{1}{2}\text{ }\mu\text{F}^{-1}
Find a common denominator and add the fractions.
3
Calculate the reciprocal to determine CeqC_{eq}
Ceq=2 μFC_{eq} = 2\text{ }\mu\text{F}
Inverting 12\frac{1}{2} yields the total equivalent capacitance.

Key Concept

Equivalent Capacitance in Series
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