Difference between Resistance and Reactance

Resistance and reactance are the two major parameters of an electric circuit element that together form the impedance of the circuit element. One most significant difference between resistance and reactance is that the resistance is the opposition in the flow of electric current offered by a circuit element called resistor, whereas the reactance is the opposition in the change in the magnitude and direction of the current and voltage offered by a circuit element called inductor or capacitor.

The combined opposition offered by the resistance and reactance in an electric circuit is known as impedance of the circuit. In this article, we will explain various difference between the resistance and reactance in detail. Also, we will explain what the resistance and reactance are, so that a reader can understand the differences between them easily.

What is Resistance?

Electrical resistance is defined as the measure of opposition offered by the material of the conductor in the path of electric current (or electric charges or electrons). It is also known as electrical friction as it slows down the motion of electrons. The circuit element which introduces resistance in the path of current is known as resistor.

According to ohm's law, when a voltage is applied across a current, an electric current starts flowing through the conductor, and the ratio of voltage across and current through remains the constant provided the physical condition such as area, length, temperature, etc. of the conductor does not change, i.e.

$$\mathrm{\frac{V}{I}\:=\:Constant}$$

This constant is known as resistance of the given conductor. The resistance is denoted by 'R' and is measured in Ohms (Ω).

Also, for the given conductor, let

$$𝑙l\:=\:\mathrm{length \:in\: meters}$$ 

$$a\:=\:\mathrm{Area\:of \:cross \:section \:in \:m^2}$$

Then, the resistance can also be defined in terms of physical dimensions as,

$$\mathrm{Resistannce\:,R\alpha\:\frac{l}{a}}$$

Where, "ρ" is the resistivity of the conductor.

What is Reactance?

The reactance is defined as the opposition that an electric circuit component exhibits to the change in the electric current (alternating current) due to inductance and capacitance present in the circuit. The reactance is denoted by letter X and is measured in Ohms.

There are two circuit elements that are used to introduce the reactance in a circuit viz. Inductor and Capacitor.

The reactance offered by the inductor to the flow of electric current is called inductive reactance and it is denoted by XL. Similarly, the reactance offered by a capacitor is termed as capacitive reactance and is denoted by XC. The reactance due to inductance and capacitance be given by the following relations:

$$\mathrm{Inductive\:reactance},X_L\:=\:\omega{L}\:=\:2fL$$ 

$$\mathrm{Capacitive\:reactance},X_c\:=\:\frac{1}{\omega{C}}\:=\frac{1}{2\pi{fc}}$$

Therefore, it can be seen that the reactance is directly proportional to the supply frequency in case of inductive circuit and it is inversely proportional to the frequency in case of capacitive circuit.

Difference between Resistance and Reactance

The major differences between resistance and reactance are highlighted in the following table −

Basis of Difference	Resistance	Reactance
Definition	Resistance is the measure of opposition offered by a conductor in the flow of electric current.	Reactance is the opposition to the flow of alternating current which opposes any change in the magnitude and direction of the current.
Circuit element	The circuit element which offers resistance in the circuit is called resistor.	The circuit elements responsible for the reactance in the circuit are: Inductor and Capacitor.
Denotation	Resistance is denoted by letter 'R'.	Reactance is denoted by letter 'X'. For inductive circuit, it is denoted by XL and for capacitive circuit, it is denoted by XC.
Formula	Resistance is given by,$$R\:=\:\frac{\rho{l}}{a}$$	$$\mathrm{Inductive\:reactance},X_L\:=\:\omega{L}\:=\:2fL$$ $$\mathrm{Capacitive\:reactance},X_c\:=\:\frac{1}{\omega{C}}\:=\frac{1}{2\pi{fc}}$$
Part of impedance	Resistance is the real part of impedance.	Reactance is the imaginary part of the impedance.
Dependency	Resistance depends upon the physical dimensions such as length, cross-sectional area, temperature, resistivity of the conductor.	Reactance is the function of supply frequency and the value of either inductance or capacitance.
Phase relationship	For a resistance, the voltage and current are in phase with each other, i.e. the phase difference is zero.	In case of reactance, the voltage and current are 90° out of phase with each other.
Effect	Resistance dissipates (or consumes) the electrical energy in the form of heat.	Reactance does not dissipate the electrical energy rather it stores the energy in the electric field (capacitor) or in magnetic field (inductor).
Circuit in which effective	Resistance is effective in both DC and AC circuits.	As reactance is the function of frequency, therefore, it specifically effective in AC circuits only.
Electric power	Resistance consumes active power or real power and dissipates it. Thus resistance cannot supply power back to the circuit.	Reactance does not dissipate the power, it stores it and return it back to the circuit.
Applications	Resistance is mainly used to control the amount of electric current in an electric circuit.	Reactance is used to control the sudden change in current and voltage in an AC circuit.

Conclusion

In this article, we have listed noticeable differences between resistance and reactance in the tabular form. Both resistance and reactance are the opposition offered in the flow (or change) of current and together are known as impedance of the circuit. However, from the above discussion, we can conclude that resistance prevents the flow of current and is effective in both AC and DC circuits, whereas the reactance prevents the change in the current and is effective in only AC circuit due to its dependency on frequency.