Resistance vs Impedance

The most important distinction between resistance and impedance is that resistance refers to direct current opposition, whereas impedance refers to alternating current. The voltage and current waveforms of the circuit are not affected by resistance, however, the current and voltage waveforms are affected by impedance.

Resistance vs Impedance

The collision of electrons in a conductor with the ionic lattice of the conductor causes resistance, resulting in the conversion of electrical energy to heat. Electrical resistance can be defined as the resistance to a constant electric current. When linked to DC, an ideal resistance changes with frequency.

Impedance is a measurement of the nature of the opposition caused by inductance and capacitance in AC electricity. The frequency affects the opposition. The terms reactance and impedance are frequently confused and used interchangeably. 

It’s vital to remember that reactance refers to the resistance that inductors and capacitors provide to AC current, whereas impedance is the sum of resistance and reactance.

Resistance 

The resistance that material provides to the flow of direct and alternating currents is the same. The letter R stands for it. Resistance can be computed using the following formula in terms of voltage (V) and current (I), R=V/I. Ohm is the SI unit of resistance.

Resistance With a Sinusoidal Supply

 If the main voltage rises and falls in a sinusoidal pattern, the current forced by the voltage will also rise and fall. Since the load is resistance, the voltage and current will both achieve their peak value or maximum and then return to zero value at the same time, that is, they will improve and decrease concurrently and are referred to as “in-phase.” 

Difference Between Resistance and Impedance | Linquip

The current that travels through the AC resistance then changes in a sinusoidal manner with time and is represented by the frequency equation I(t), where I represent the highest value of the current and θ is the phase angle coefficient. So, using Ohm’s Law, the peak voltage or maximum in R’s terminals  and the obtained current can be calculated as follows,

V(t)=R.I(t)=R.Im​.sin(ωt+θ)

iR(t)​=IR(max)​.sin(ωt)

As a result, for a given resistive system, the alternating current in the resistor varies with the applied voltage in a sinusoidal pattern. The phasors of both the current and the voltage will have the same values since the basic frequency is equal to both.

Impedance 

When thinking about impedance, as mentioned it is a concept used for AC equivalent. It oscillates like a sine wave, therefore the sign is constantly changing. This means that other factors, such as inductance and capacitance, must be taken into account. Impedance is the sum of both resistance and reactance contributions. This is critical for AC design and analysis.

Reactance

Reactance is a measurement of the type of resistance to AC power caused by capacitance or inductance. The frequency of this antagonism varies. A capacitor, for example, only enables DC current to flow for a brief time until it is charged; after that, the current will stop flowing and the capacitor will appear to be open. 

However, if a signal with a very high frequency is applied to the capacitor (a signal with a voltage that changes very quickly back and forth), the capacitor will appear to be shorted. The reactance of the capacitor is inversely proportional to frequency. The reactance of an inductor is directly related to frequency; DC flows freely but high-frequency AC is blocked.

Difference Between Resistance and Impedance

Here’s a list to shortly take a look at the basic differences. 

Basis	Resistance	Impedance
Definition	Resistance is the amount of resistance provided to the flow of electricity in an electric circuit.	Impedance is the resistance that resistance, capacitance, and inductance provide to the flow of current in an AC circuit.
Circuit	Both AC and DC circuits have resistance.	Only in an AC circuit does impedance exist.
Elements	It is the circuit’s contribution from the resistive element.	Both resistance and reactance play a role in this.
Symbol	It is designated by R.	It is designated by Z.
Real and Imaginary Value	Resistance is a basic number consisting solely of real numbers.	Impedance is a complex value that includes both real and imaginary values.
Frequency	In a circuit, resistance is constant and does not change with the frequency of AC or DC.	The frequency of AC affects the impedance.
Phase Angle	Resistance doesn’t involve phase angle.	Impedance has both magnitude and phase angle.
Power Dissipation & Energy Stored	If kept in an electromagnetic field, it just signifies power dissipation in any material.	It shows both power loss and energy storage when kept in an electromagnetic field.

Conclusion

Impedance and resistance both are very important in electrical circuitry. Both work as a resistance to the flow of current, but the phenomenon is very different. From the basic definition, elements, and mechanism to power dissipation, the distinction between them is quite prominent.