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# What is Impedance and is it important?

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#### Cisco

##### Newbie level 6
Can some explain to me what is impendance and why is it important to know impedance?

Electrical impedance a measure of opposition to alternating current (AC). Electrical impedance extends the concept of resistance to AC circuits, describing not only the relative amplitudes of the voltage and current, but also the relative phases. When the circuit is driven with direct current (DC), there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle.
Electrical impedance - Wikipedia, the free encyclopedia

Impedance matching is required for maximum power transfer.
Maximum power transfer theorem - Wikipedia, the free encyclopedia
Impedance plays important role in determining circuit characteristics like gain, bandwidth etc.

Cisco

### Cisco

Points: 2

#### beechy

##### Newbie level 1
Wow- that's the best expanation I have ever seen - seriously. It's made it clearer in my mind too

#### ElectronicsRookie

##### Member level 1
Resistance is the opposition to electron flow in the wire. The opposition results in heat generated in the material of the resistor. The flow of electrons in the wire is reduced. It is common in DC current and AC current. Components are usually resistors.
Reactance is the opposition to electron flow however there is no dissipation of energy but conservation which results in delay of electron flow. It is common in AC current. Components are usually capacitors and inductors.
Impedance is a sum of resistance and reactance. When you have a circuit with impedance it means that it has resistance and reactance. Therefore the circuit has resistor components and capacitive and/or inductive components. Note that diodes, transistors and myriad of other components have some reactive, resistive or impedance behaviour.

Cisco

### Cisco

Points: 2

#### abhikohli

##### Member level 2
Impedance is a sum of resistance and reactance.