When we talk of impedance vs resistance we are simply referring to the differences and similarities that exist between impedance vs resistance. In this article, we will look at what resistance, impedance are. 

impedance vs resistance
impedance vs resistance

We will also explain their concept, the formula applicable to each. Mention the differences  between impedance vs resistance, and also have a look at their similarities. We will also solve a few problems on impedance and resistance. 

What is a Resistance?

Resistance is the opposition to the flow of current or charges (electrons). The s.i unit of resistance is ohm. We can write the symbol for ohm as Ω. Resistance takes place in a direct current (D.C) circuit.

The unit of resistance is named after a scientist George Simon Ohm. George Ohm investigates the relationship between the potential difference between the edges of a wire and the current flowing through the wire.

The above introduction will now lead us to the explanation of ohm’s law to better understand the concept of resistance.

What is Ohm’s Law?

Ohm’s law stated that the current flowing through a conductor, be it a wire, is directly proportional to the voltage (potential difference) across its ends, provided other physical properties of the conductor remain constant.

The mathematical formula for the above law is

I ∝ V

Which can be rewritten as 

I = VR

Where R is the resistance and a proportionality constant.

Base on the formula I = VR, we can make R subject of the formula such that

R = V / I

From the above formula

R is the resistance and its unit is in ohm (Ω)

V is the voltage and its unit is in volts (v)

I is the current and its unit is in ampere (A)

We can also say that resistance is the ratio of potential difference to current flowing in the circuit. Ohm’s law is not obeyed by such conductors as radio valves (e.g diodes), transistors, rectifiers, and gases.

What is Impedance?

Impedance (Z) is the overall opposition of a mixed circuit containing a resistor, an inductor and/or a capacitor. We also measure impedance in ohms (Ω). Unlike resistance, Impedance takes place in an alternating current (a.c) circuit. 

The formula for calculating impedance is

Z2 = √ R2 + (Xc2 – XL2


Z = Impedance

R = Resistance

Xc = Capacitive reactance

XL = Inductive reactance

Like I mentioned earlier, the s.i unit of impedance is in ohms

Therefore, we can say that the potential difference is

V = IZ

Which shows that the impedance is

Z = V / I

We can equally say that impedance is a measure of how much a circuit resist the flow of alternating current. Impedance consist of resistance, inductance, and capacitance. Also, the voltage and current in an impedance represents sine wave.

Differences: Impedance vs Resistance

The major difference between impedance and resistance are:

– Is the measure of the total opposition of the current flow in a circuit that includes both resistance and reactance
– The symbol of impedance is Z
– Resist the flow of alternating current in a circuit
– Its a measure of how much a material or component opposes the flow of electric current through it
– The symbol of resistance is R
– Resist the flow direct current in a circuit
Differences: Impedance vs Resistance

Similarities Between Impedance and Resistance

Here are the similarities between impedance and resistance:

  1. The s.i unit of impedance and resistance is in ohms (Ω)
  2. Both impedance and resistance are due to the resistance of the flow of current.
  3. They play an important role in the design of electronic circuits.
  4. They are both the ratio of current to voltage

Solved Problem

  1. An alternating current supply of 240 volts is connected across a capacitor of 5 micro faraday and resistance of 50 ohms in series at 50 Hz. Find

a. Capacitive reactance

b. Impedance


a. Capacitive reactance = Xc = 1 / 2πfC = 1 / (2 x 3.142 x 50 x 5 x 10-6)


Xc = 637 Ω

b. Impedance, Z = √ R2 + Xc2 

Z = √(R2 + Xc2) = √(502 + 6372) = 639 Ω

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