## Main Difference – Impedance vs. Resistance

Impedance and resistance** **are terms that describe an opposition to a current’s flow through a circuit. The **main difference** between impedance and resistance is that **resistance is a property that depends only on the material that the component is made of**, **its dimensions and the temperature**. For ideal conductors, a change in current through the component does not cause a change in the resistance of that component. **Impedance encompasses not only resistance but also** **reactance**: the property that describes how a component opposes any *changes* in the current, such as the change in current in AC circuits.

## What is Resistance

Resistance is defined as the ratio of potential difference across a component to the current through that component:

Resistance originates when electrons flowing across a conductor collides with lattice ions in the material. Therefore, resistance depends on the resistivity of the material and the dimensions of the component. Resistance also changes with temperature because temperature affects the energy of lattice ions and the electrons. If you connect a resistor to an AC circuit and change the frequency of the AC supply, the resistance of the resistor is not going to change.

## What is Impedance

**Capacitors and inductors** are components with **reactance**. This is a property that causes them to oppose *changes* in current when they are connected in AC circuits. Reactance depends on the frequency of the AC current. For example, for a capacitor with capacitance in an AC circuit with a frequency , the **capacitive reactance** is given by

For an inductor with inductance , it is given by

Impedance is a quantity that takes into account both resistance *and* reactance. It is commonly expressed as a complex number because it is composed of a part that does not change (resistance, making up the *real* part of the number) and also a part that changes periodically (reactance, making up the *imaginary* part of the number).

The **complex impedance** () is given by:

The **magnitude of an impedance** is given by .

The **phase angle of an impedance** (how much the current will lag behind the voltage) is given by

For example, for the circuit shown below

The magnitude of impedance is .

Phase angle is .

## Difference Between Impedance and Resistance

### Type of Measurement

**Resistance** does not take into account the opposition to changes in current. Resistance is a property that depends only on the material that the component is made of, its dimensions and the temperature.

**Impedance** takes into account both resistance as well as reactance (opposition when current changes).

### Type of Circuit

**Resistance** is a property of both AC and DC circuits.

For a DC circuit,** Impedance** is simply its resistance. For an AC circuit, it is a quantity that changes with the frequency of the AC current.