Capacitors in Parallel and Series

Capacitors and parallel and series capacitance

Capacitors in Parallel

capacitors in parallel

For parallel-connected capacitors the equivalent capacitance can be expressed as

C = C1 + C2 + . . + Cn         (1)

where

C = capacitance (Farad, F, μF)

It is common to use µF.

Capacitors in Series

capacitors in series

For series-connected capacitors the equivalent capacitance can be expressed as

1/C = 1/C1 + 1/C2 + . . + 1/Cn         (2)

Example - Capacitors Connected in Parallel and in Series

The equivalent capacitance of two capacitors with capacitance 10 μF and 20 μF  can be calculated as

in parallel

C = (10 μF) + (20 μF)

    = 30 (μF)

in series

1/C = 1/(10 μF) + 1/(20 μF)

    = 0.15 (1/μF)

or

C = 1 / 0.15 (1/μF)

    = 6.7 (μF)

Capacitance of Two Coaxial Cylinders

C = 2 π εo εr l / ln(r2/r1)   (3)

where

εo = absolute permittivity, vacuum permittivity (8.85 10-12 F/m, Farad/m)

εr = relative permittivity

l = length of cylinders

r2 = radius of inner cylinder

r1 = radius of outer cylinder

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