Table of Contents

**Introduction:**

**Reactance and Impedance: **Due to the fact that current flows in only one direction and resistance is the main component of the circuit, DC circuits are comparatively simple to evaluate. AC circuits, on the other hand, are more difficult to understand since voltage and current alternate directions at a set frequency.

In contrast to DC circuits, AC circuits frequently feature both resistance as well as another property known as reactance. Resistance and reactance are combined to form impedance.

The amplitude and phase variations of sinusoidal alternating current (AC) passing through a circuit element are computed using reactance. Reactance is measured in ohms, similarly to resistance, with positive numbers indicating inductive reactance and negative ones indicating capacitive reactance. The letter X stands for it.

**A brief outline:**

**Inductors and capacitors both have reactance, **which is a feature that resists a change in current. Reactance is particular to AC power and varies with the current because it only impacts changing current. Reactance causes a 90-degree phase shift between voltage and current, regardless of whether the component is an inductor or a capacitor.

**Inductive reactance **is the reaction that occurs in an inductor. Energy is stored in the form of a changing magnetic field when inductive reactance is present, and the current waveform delays the voltage waveform by 90 degrees.

**Capacitive reactance** is the reaction that occurs in a capacitor. Capacitive reactance stores energy as a shifting electrical field, causing current to trail voltage by 90 degrees. When two conducting plates are arranged parallel to each other with a small gap between them and filled with a dielectric material, capacitance is generated (insulator).

**Impedance** is a complex quantity that contains both real and imaginary parts and is made up of resistance and reactance (both inductive and capacitive). The magnitude and phase of impedance are both present.

**Important concepts:**

**What is the definition of reactivity?**

The inertia against the motion of electrons in an electrical system, or the property against by the electron flow in an electrical circuit, is referred to as reactance.

It is symbolized by the letter R and is quantified in ohms (the Greek sign for resistance). It is the mathematical ratio of the potential difference V to the current flows between two sites in an electrical circuit.

**R = VI**

It’s also known as an electrical circuit’s phantom resistance. The current generation in an electrical circuit is caused by electron mobility, while reactance is caused by inertia against electron motion. It is mostly caused by the inductance or capacitance of the parts. It resists changes in the element’s current in a magnetic field and resists changes in the element’s voltage in an electric field. Its unit of measurement is the Greek symbol ohm, and it is mathematically denoted by the letter X.

**The Different Types of Reactions:**

**Reactance can be divided into two categories:**

- Reactance capacitive (Ohms is the unit)
- Reactance inductive (Ohms is the unit)

Capacitive Reaction is a term that refers to the,

**X**_{c}** = 1/2ПfC**

Where,

- XC is the capacitive reactance
- f is the frequency of AC power supply
- C is the capacitance

When a capacitor is connected with an AC supply, the capacitor voltage and current do not vary at the same time. The AC power supply determines the potential difference across the capacitor. The graph below depicts the change in the present and potential differences. When the potential difference is zero, the current is at its maximum.

**What is the concept of impedance?**

Impedance is the result of combining resistance and reactance. It’s basically anything that prevents electrons from flowing freely via an electrical circuit.

As a result, it has an impact on the current generation in the electrical circuit. It can be found in all potential circuit components and in all possible electrical circuits. Impedance is represented mathematically by the letter Z, and its unit is the ohm. It’s a combination of both resistance and reactance.

**Significance of Reactance and Impedance in NEET exam:**

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Also read: **Important Topic of Physics: Faraday’s Law**

**Frequently asked questions (FAQs):**

**Question 1: What is a wattless current, and how would it work?**

**Answer: **A wattless current is a component of an AC current that utilizes no energy in a circuit. The following calculation can be used to calculate the average energy dissipated by the AC circuit:

**P = VI cos Φ**

It can be observed that the average power dissipated in a circuit is affected not only by the voltage and current but also by the phase angle that exists between them.

The phase shift between voltage and current in a circuit with only a capacitor or inductor is /2. As a result, the cos becomes zero, and the power which has been dissipated becomes zero as well.

**Question 2: When do I use impedance rather than reactance, and when should I use reactance instead of impedance?**

**Answer**: Voltage and current have a phase difference, and impedance is frequency sensitive. The resistance of an ideal coil at a given frequency is measured by reluctance. The resistance of an ideal capacitor at a given frequency is measured via reactance.

As an engineer, I know that coils are flawed, that wire has an inherent resistance, and that loops produce capacitance. A coil’s impedance is determined by the combination of resistance, reactance, and reluctance. Wire wound resistors have inductance to offer minimal reluctance, while some surface mount resistors have modest capacitance.