# Difference between resistance and impedance

When we speak about DC electricity, resistance is the term used to refer to opposition to current flow whereas impedance is the term used in AC electricity. Impedance is basically a combination of resistance and reactance. Here is the difference between resistance and impedance.

## Resistance

Resistance is the term used to denote the opposition to the flow of current in a circuit or material. It depends on the resistivity and dimensions of the material. The resistance offered by a material to the flow of direct current and alternating current remains the same. It is denoted by the letter R.

Where ‘ρ‘ is the resistivity of the object, ‘l‘ is the length of the object and ‘A‘ is its area.

In terms of voltage (V) and current (I), resistance can be calculated using the following formula:

The SI unit of resistance is Ohm.

## Impedance

Impedance is the opposition to alternating current. It is a combination of resistance and reactance. It is represented by a complex number and has a real and an imaginary part. The real part represents resistance and the imaginary part represents the reactance. Reactance can be capacitive, reactive or a combination of both.

Where, Z is the magnitude of impedance, R is the resistance and XT is the total reactance. The SI unit of impedance is Ohm.

## Difference between resistance and impedance

To understand the difference between resistance and impedance better, lets compare both of them side by side.