What is Capacitive Reactance : Working & Its Applications

In a circuit, reactance is the opposition that is offered through a capacitor (C) & inductor (L) to the AC current flow. It is much related to resistance however reactance changes through the frequency of the voltage source and it is measured in ohms (Ω) and reactance is very complex than resistance in nature, because its value mainly depends on the frequency of the signal flowing throughout the capacitor. These are available in two types like capacitive reactance (XC) & inductive reactance (XL). So this article discusses an overview of capacitive reactance and its working with applications.

What is Capacitive Reactance?

The capacitive reactance can be defined as; in an AC circuit, the opposition offered from a capacitor to the ac current supply. A capacitor resists the changes within the potential difference otherwise the voltage across its two plates. It is inversely proportional to the signal frequency & capacitance. It is generally represented through ‘Xc’ & measured in ohms (Ω).

How does a Capacitive Work?

A capacitor is a passive component used to store electric energy from an energy source like a battery. It includes two terminals which are separated by an insulator (dielectric material) and connected to two metal plates. Once it is activated, the capacitor releases electricity quickly in a fraction of a second.

Capacitive Reactance in AC Circuit

In the AC circuit, the flow of current through the capacitor (C) is directly proportional to the rate of change of the voltage supply. If a sine wave is used in the voltage supply, then the cosine wave is used in current. But, the flow of current throughout the AC circuit will be opposed through some resistance. So this type of opposition toward the current flow is known as capacitive reactance. So, the capacitor has capacitive reactance in AC circuits.

AC Circuit
AC Circuit

So, it is available in capacitor-based AC circuits only. In AC circuits, the capacitance of the capacitor mainly depends on the positive & negative half cycles of the voltage supply. It mainly depends on the frequency of the voltage supply. The capacitive reactance formula can be given as

Capacitive Reactance (Xc) = 1/2πfC

Where, π = 3.14

F= frequency in Hertz (Hz)

C = Capacitance in faradays (F)

In the above equation, 2πƒ can also be written in the Greek letter ‘ω’ to indicate an angular frequency. From the above formula, it can be observed that if wither capacitance or frequency is increased then the overall capacitive reactance can be decreased.

When the frequency approaches infinity then the reactance of the capacitor will decrease to zero so that it acts as a perfect conductor.

But, when the frequency approaches zero otherwise DC, then capacitors reactance will increase to infinity which acts like huge resistance. So finally, the capacitive reactance (Xc) is inversely proportional to frequency (f) for any capacitance value.

Capacitive Reactance in Series

When capacitors are connected in series, then the whole capacitance is below one of the connected capacitors’ capacitances. If a minimum of two or above capacitors are connected in series then the overall effect is that of a single capacitor including the total amount of the plate spacing of the separate capacitors.

Ctotal = 1/1/C1+1/C2 +…+1/Cin

Capacitive Reactance in Parallel

When capacitors are connected in parallel, the whole capacitance is the number of the individual capacitors’ capacitances. If two or above capacitors are connected parallel, then the overall effect is that of a single equivalent capacitor including the total amount of the plate areas of the separate capacitors.

Ctotal = C1+C2+…+Cin

Capacitive Reactance in Series & Parallel
Capacitive Reactance in Series & Parallel

Please refer to this link to know more about capacitors in series and parallel

Example:

The three capacitors in a circuit like C1 = 10 µF, C2 = 20 µF & C3 = 25µF are connected to a 60Hz source, then what is the capacitive reactance (Xc) when capacitors are connected in series and parallel?

For Series Capacitors:

We know the values for series connection circuit be like C1 = 10 µF, C2 = 20 µF & C3 = 25µF.

Capacitors in Series Connection
Capacitors in Series Connection

When capacitors are connected in series then Ctotal = 1/1/C1+1/C2 +1/C3

1/ C1 = 1/10 = 0.1

1/C2 = 1/20 = 0.05

1/C3 = 1/25 = 0.04

Ctotal = 1/1/C1+1/C2 +1/C3 => 1/0.1+0.05+0.04

Ctotal =.1/0.19 = 5.26 µF

For Parallel Capacitors:

We know the values for parallel connection circuit be like C1 = 10 µF, C2 = 20 µF & C3 = 25µF.

Capacitors in Parallel Connection
Capacitors in Parallel Connection

When capacitors are connected in parallel then Ctotal = C1+C2 +C3

Ctotal = 10+20+25 = 55 µF

Capacitive Reactance Vs Frequency Graph

The characteristics between capacitive reactance and frequency are shown below, In the following graph, the capacitor’s capacitive reactance decreases when the frequency supply of the voltage supply increases in the circuit. So, this clearly states that capacitive reactance is inversely proportional to the frequency supply for the applied AC signal.

Capacitive Reactance vs Frequency
Capacitive Reactance vs Frequency

In addition, once the frequency supply of the voltage supply used in the AC circuit enhances then the flow of current within the AC circuit increases linearly. So, the flow of current increase in the AC circuit mainly occurs due to the change in voltage across the two capacitor plates.

Capacitive Reactance Vs Inductive Reactance

The difference between capacitive reactance and inductive reactance includes the following.

Capacitive Reactance

Inductive Reactance

Capacitive reactance is frequently connected through the electric field that changes in between two conducting plates that are arranged separately from each other by insulating material. Inductive reactance is associated generally with the magnetic field nearby a current-carrying wire.
It is denoted with ‘XC Inductive reactance is denoted with ‘XL
The unit of capacitive reactance is ‘Ohms’ The unit of inductive reactance is ‘Ohms’
It can be formed because of the capacitor which is known as a capacitive element. It can be formed because of the inductor which is known as the inductive element.
Its formula is Xc =  1/2πfC Its formula formula is XL =  2πfL
The function of the capacitive elements is to store electrical energy in an electric field form. The function of an inductive element is to store electrical energy in a magnetic field form.
It is generated because of the voltage opposition across the capacitors. It is generated because of the current opposition across the inductor.
It will create a lag between voltage and current. It will create a power lag in between the waveforms of voltage and current.

Applications

The applications of capacitive reactance include the following.

  • It is used in different circuits like AC filters or in smoothing circuits of DC power supply to decrease unwanted ripple voltage effects because the capacitor applies a short circuit signal lane to any unnecessary frequency signals on the o/p terminals.
  • The capacitive reactance is used to block DC but provides less reactance for AC.
  • For AC or DC circuits, resistance remains the same but capacitive reactance depends on frequency.
  • The required capacitance (C) becomes lesser for higher frequencies.

What is the role of capacitive reactance?

The main role of capacitive reactance is a measure of how a capacitor limits the flow of AC. It is measured in ohms.

Why do capacitors block low frequencies?

A capacitor is a reactive device, so it blocks low frequencies like DC and allows high frequencies like AC. A capacitor has high impedance/resistance for low-frequency signals, so these signals are blocked.

How does capacitive reactance XC vary with frequency?

The capacitive reactance (Xc) of a capacitor reduces when the frequency across its two plates enhances. So, capacitive reactance (Xc) is inversely proportional to frequency.

What is the effect of capacitive reactance?

The effect of capacitive reactance is to cause the flow of current to guide the voltage.

What are the combined effects of resistance inductive reactance and capacitive reactance?

The combined effect of resistance and reactance like inductive & capacitive makes up the whole opposition to the flow of current in an ac circuit which is known as impedance (Z). The impedance can be measured in ohm.

What is the total capacitive reactance?

The total reactance is the sum of individual reactances. So the capacitive reactance (X) of a capacitor (C) can be measured by using this formula like Xc = 1/2 πfc.

Thus, this is all about an overview of capacitive reactance. So, this reactance prevents the DC component of a signal from supplying though, other than it will affect the alternating signal that may emerge. Capacitors are used in several electronic and electrical circuit designs, so calculating the reactance level is very important. Here is a question for you, what are the advantages and disadvantages of capacitive reactance?

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