Calculate the reactance

*X*

_{C}. Choosing a capacitor

*C*and frequency

*f*is best.

Capacitive reactance (symbol

*X*

_{C}) is a measure of a capacitor's opposition to

AC (alternating current). Like resistance it is measured in ohms, but

reactance is more complex than resistance because its value depends on the

frequency (

*f*) of the electrical signal passing through the capacitor as well

as on the capacitance,

*C*.

Capacitive reactance,

*X*

_{C}= 1 / (2 × π ×

*f*×

*C*)

where:

*X*

_{C}= reactance in ohms (ohm),

*f*= frequency in hertz (Hz),

*C*= capacitance in farads (F)

The reactance

*X*

_{C}is large at low frequencies and small at high frequencies.

For steady DC which is zero frequency,

*X*

_{C}is infinite (total opposition),

hence the rule that capacitors pass AC but block DC.

For example a 1 µF capacitor has a reactance of 3.2 kΩ for a 50 Hz signal, but

when the frequency is higher at 10 kHz its reactance is only 16 Ω.

**Capacitance**

*C***, frequency**

*f***, and capacitive reactance**

*X*_{C}

Enter the values for capacitance and frequency, then press "calculate".

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