Difference between Resistance and Impedance

In this article, we will discuss all the significant differences between resistance and impedance, i.e. resistance vs impedance.

What is Resistance?

The measure of opposition offered by a material in the flow of electric current is called resistance. Resistance is denoted by the letter R, and its SI unit is Ohm (Ω).

Resistance is also known as electrical friction because it results in the production of heat when current flows through the material. The circuit element that is used to model resistance in an electric circuit is called a resistor. Resistance is one of the fundamental parameters in every electrical and electronic circuit.

Resistance of a conductor is given by,

`\R=ρl/a`

Where ρ is the resistivity or specific resistance of the material, l is the length of the conductor, and a is the area of the cross-section.

Resistance of an electric circuit equally opposes the direct as well as alternating current.

What is Impedance?

The total opposition offered by circuit elements of an electric circuit in the flow of alternating current is called impedance. Therefore, the term “impedance” only specifies the total opposition in an AC circuit.

Impedance is denoted by the letter Z and it is measured in Ohm (Ω). Impedance is a complex quantity as it has two components namely, real and imaginary. The real part represents the resistance of an AC circuit, and the imaginary part represents the reactance of the AC circuit.

Therefore, the impedance of an AC electric circuit is given by,

`\Z=R+jX`

Where R is the resistance of the circuit and X is the reactance of the circuit.

After getting an overview of resistance and impedance, let us now discuss their differences.

Difference between Resistance and Impedance

The following table gives the important differences between resistance and impedance:

Basis of comparison	Resistance	Impedance
Basic Definition	The property of a material that restricts the flow of electric current through it is called resistance.	The total opposition offered by different circuit elements in the flow of alternating current (AC) is called impedance.
Denotation	Resistance is denoted by the letter R.	Impedance is denoted by the letter Z.
Type of circuit	Resistance is applicable in both DC and AC circuits.	Impedance is significant in AC circuits only.
Type of quantity	Resistance is a real quantity. Hence, it has magnitude only.	Impedance is a complex quantity. Hence, it has both magnitude and phase.
Circuit components	The circuit component used to implement resistance in a circuit is a resistor.	The impedance is offered by a combination of circuit components, such as resistors, inductors, and capacitors.
Frequency dependence	The resistance of an electric circuit is independent of the supply frequency.	The impendence of an electric circuit is the function of frequency.
Phase shift between I and V	In the case of resistance, there is no phase difference between voltage and current, i.e. phase difference is zero.	In the case of impedance, there is a certain phase difference between voltage and current that depends upon the value of the reactive component.
Power factor	In the case of resistance, the power factor is always unity.	Impedance can cause a unity, leading, or lagging power factor depending on the value of real and imaginary components.
Addition	We can add two or more resistances arithmetically.	Two or more impedances cannot be added arithmetically, instead, they are added as per phasor algebra.
Power	Resistance always consumes power. This is called active power.	Impedance consumes as well as stores power. In the case of impedance, three types of powers are active power, reactive power, and apparent power.
Applications	Resistance is used to control the flow of electric current in a DC or AC circuit.	Impedance is used to control the flow of current in an AC circuit.

Conclusion

In conclusion, this is all about the important differences between resistance and impedance. In the above table, we discussed all the significant differences between resistance and impedance. However, both resistance and impedance are the measures of opposition in the flow of electric current in electric circuits.