Inductive Reactance and Capacitive Reactance

What is Capacitive Reactance?

The capacitive reactance can be defined as the reactance that is produced because of the capacitive elements (Capacitors). We can denote it as. The capacitive reactance is an opposition of the voltage across the capacitive element which is temporarily used to store electrical energy in the form of an electric field. The capacitive reactance creates a phase difference between the current and the voltage.

 

In the capacitive circuit, voltage is lead by the current. For an ideal capacitive circuit, the voltage lead by the current is. Thanks to capacitive reactance, due to which the power factor of the system or circuit leads. The phasor diagram for the ideal capacitance circuit is drawn below.

 

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Difference Between Reactance and Resistance

  1. The reactance is a component of impedance while the resistance is a DC component of Resistance.

  2. The value of reactance is always a complex number whereas the value of resistance has to be a real number.

  3. In a purely inductive or capacitive circuit, the resistance will be zero and in a purely resistive circuit, the reactance will be zero.

  4. Due to reactance, both amplitude, as well as the phase of current, will change. Due to resistance, the current and voltage will always remain in phase.

  5. The value of reactance is dependent on the supply frequency whereas the value of resistance is not dependent on the supply frequency.

  6. For a DC supply, the inductive reactance has to be zero and the capacitive reactance will be infinite. For DC supply, the resistance will remain the same.

  7. Reactances are denoted as and. Resistance is denoted as.

  8. The power factor in reactance is leading or lagging due to the reactance element. In Resistance, the power is unity when the reactance is zero.

Solved Examples Inductive Reactance and Capacitive Reactance

What Is An Electrical Reactance?
An electrical reactance can be defined as a flow that is opposite in the direction of current in a circuit element because of its inductance and capacitance. If the reactance is greater, then the current will be smaller for the same applied voltage. Reactance being almost similar to electric resistance also differs from it in a few ways. When an alternating current is made to pass through the electric circuit or element, both the phase as well as the amplitude of current will change. Also, the energy is stored in the element containing reactance.


The energy is thus released either in the form of an electric field or a magnetic field. The reactance in the magnetic field resists change in the current whereas, in the electric field, the reactance will resist the change in voltage. If the reactance releases energy in the form of a magnetic field, it is called inductive reactance whereas if the reactance releases energy in the form of an electric field, it is called capacitive reactance. With the increase in frequency, capacitive reactance is decreased, and inductive reactance is increased. An ideal resistor will have zero reactance, whereas ideal inductors and capacitors will have zero resistance.

What is Inductive Reactance?

The inductive reactance is the reactance that is produced due to the inductive element (inductor). It can be denoted as. With the help of inductive elements, electrical energy can be stored in the form of a magnetic field. When an alternating current is passed through the circuit, the magnetic field is formed around it which can be changed as a result of the current. Changes in the magnetic field can induce another electric current in the same circuit. Lenz's law states that the direction of this current is opposite to the main current. Therefore, we can say that the inductive reactance actually opposes the change of current through the element.

 

The current flow due to the inductive reactance results in the delay which may result in creating the phase difference between the current and the voltage waveforms. The current for the inductive circuit may lag the voltage. In an ideal inductive circuit, the current lags voltage by. The inductive reactance is also the reason why the power factor is lagging. The phasor diagram for the ideal inductive circuit is drawn below.

 

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The Phasor Diagram of Ideal Inductive Circuit

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To empower students to study smart and give their best, Vedantu outlines the definitions and solved examples to best illustrate the topic of Inductive Reactance and Capacitive Reactance. This resource is especially useful when students wish to have a quick read-through of topics and solve their doubts regarding the kind of questions that might be asked in the JEE Mains. Students should be aware that every topic is of importance not only for the examination but for their future careers as well. 

What is Electrical, Inductive and Capacitive Reactance? 

1. Electrical Reactance - It is defined as a flow that flows in the direction opposite to the flow of current in the electrical circuit. The greater the reactance, the smaller the current will be for that applied voltage. Reactance behaves differently in magnetic and electrical fields. In the magnetic field, reactance will resist change in current while it resists change in voltage in the electrical field. 


2. Inductive Reactance - Denoted by the symbol XL, it is created due to the presence of the inductive element, i.e. the inductor. One of the uses of an inductive element is that it can be used to store electrical energy in the form of a magnetic field. A particular law called Lenz's law clearly states that the direction of the current produced due to inductive reactance is opposite to the direction of the main current. This could result in creating a power lag between the waveforms of voltage and current.


3. Capacitive Reactance - Denoted by the symbol XC, it is created due to the presence of the capacitive element, i.e. the capacitors. The capacitive element helps store electrical energy in the form of an electric field, unlike the inductive element. Capacitive reactance is produced due to the opposition of voltage across the capacitors. This too creates a lag between current and voltage. The ideal lag in an inductive circuit and the ideal voltage lead by the current for a capacitive circuit is 90 degrees.

FAQs on Inductive Reactance and Capacitive Reactance

1. What are the formulae and units for inductive and capacitive reactance?

Because inductive reactance and frequency are directly proportional to each other when one increases the other also increases. Hence inductive reactance depends on both the frequency and inductance of an inductor. It is denoted by the unit XL. Its formula is depicted as -  


XL = 2πfL. It is measured in Ohms (Ω).


On the other hand, capacitive reactance is inversely proportional to the frequency and capacitance of a capacitive circuit or the capacitive element. Hence, if the reactance increases, then the frequency will decrease and vice versa. Capacitive reactance is denoted by the unit XC. Its formula is depicted as  


XC =   \[\frac {1}{2fc}\] . It is measured in Ohms (Ω). 

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If students follow these tips studiously, then cracking JEE won’t be a big deal at all. The first step is to spend some time studying the syllabus inside out. Once you have a detailed understanding of the syllabus you can jot down which topics need more practice and which ones you are familiar with. This will help you map out an effective study plan. For entrance exam preparations, books play a crucial role. Choose the best ones on the market! 


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3. What are the common questions that can be asked from reactance? 

Our resources exhaustively cover what is important under inductive and capacitive reactance. These topics form a part of a larger advanced subject called electrochemistry. Students can expect questions on the definitions and key properties of electrical reactance, inductive and capacitive reactance, problems based on these concepts and sketching of diagrams such as the AC Circuit Phasor Diagram. Students can also expect questions based on the circuit diagrams. 

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Vedantu provides the choicest of resources to students as aids to one of the most important competitive entrance examinations of their lives. Details regarding JEE Mains and JEE Advanced are periodically updated and can be accessed on this page. Vedantu has prepared step-by-step solutions for JEE Question Papers right from 2014 to 2021. They are the perfect guide as students attempt to solve question papers from previous years. The portal also has JEE Advanced Question Papers, Sample Papers, Online Mock Test Series and more! Click here to explore and download.

5. What is the difference between resistance and reactance? 

The value of reactance is represented by a complex number while that of resistance is a real number. In an inductive or capacitive circuit, the resistance is always zero and in a resistive circuit, the reactance is always zero. Another key difference is that reactance depends upon supply frequency where resistance is independent of the same. 

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