In [electrical engineering](https://en.wikipedia.org/wiki/Electrical_engineering "Electrical engineering"), **impedance** is the opposition to [alternating current](https://en.wikipedia.org/wiki/Alternating_current "Alternating current") presented by the combined effect of [resistance](https://en.wikipedia.org/wiki/Electrical_resistance "Electrical resistance") and [reactance](https://en.wikipedia.org/wiki/Electrical_reactance "Electrical reactance") in a [circuit](https://en.wikipedia.org/wiki/Electrical_circuit "Electrical circuit").
**Voltage**, **electric potential difference**, **electric pressure** or **electric tension** is the difference in [electric potential](https://en.wikipedia.org/wiki/Electric_potential "Electric potential") between two points.
The **electrical resistance** of an object is a measure of its opposition to the flow of [electric current](https://en.wikipedia.org/wiki/Electric_current "Electric current").
**Capacitance** is the ability of a component or circuit to collect and store energy in the form of an electrical charge.
## Inductance (L)
**Inductance** is the tendency of an [electrical conductor](https://en.wikipedia.org/wiki/Electrical_conductor "Electrical conductor") to oppose a change in the [electric current](https://en.wikipedia.org/wiki/Electric_current "Electric current") flowing through it.
When electricity was discovered people thought the electrons flow from the positive terminal to the negative, in actuality they flow in the opposite direction, but it is still possible to calculate the flow with the old way.
## Reactive Components
A component is a **reactive component** when it resists to changes in current or voltage.
