Basic Electrical Quantities and Properties

Volts

(V)

Other common values:

millivolt (mV)

microvolt (µV)

kilovolt (kV)

Amp

(A)

Other common values:

milliamp (mA)

kiloamp (kA)

Watt

(W)

Other common values:

milliwatt (mW)

kilowatt (kW)

megawatt (MW)

Ohm

(Ω)

Other common values:

kiloohm (kΩ)

megaohm (MΩ)

gigaohm (GΩ)

Reactance, abbreviated X

Inductors supply inductive reactance (XL)

Capacitors supply capacitive reactance (XC)

X is measured in Ω and kΩ

Impedance, abbreviated Z.

Z is measured in Ω and kΩ

AC circuits only

A transformer.

AC voltage only. The transformer is an inductor, transferring energy by generating a fluctuating magnetic filed that must constantly rise and fall to drive current.

This will not work with DC voltage.

The total resistance will increase, and the total current will decrease.

Since the supply voltage did not change, but the current decreased, the total power dissipation will also decrease.

The total resistance will decrease, and the total current will increase.

Since the supply voltage did not change, but the current increased, the total power dissipation will also increase.

As frequency increases, the capacitive reactance (and overall circuit impedance) will decrease.

As frequency increases, the inductive reactance (and overall circuit impedance) will increase.

Voltage is the driving force, caused by the potential energy of a chemical or mechanical reaction, that causes electrons to conduct if given a continuous path (circuit). Sometimes called ‘electro-motive force’, EMF, or simply E.

Current is the collective unified motion of electrons past a point in a wire, driven by a voltage, and only occurring if given a path, or circuit, from one side of the potential energy source to the other.

Resistance is the opposition to the flow of electrons by causing a change in the form of energy from electrical energy into some other form (commonly heat or light), increasing the voltage required to drive the current.

Power is the work done, or the energy consumed over a given period of time. Power can be delivered, or supplied into a circuit or system. Power will almost certainly be lost within any real system (efficiency), and as the energy is converted from electrical energy into light, heat, or motion by the ‘load device’, we say the power is dissipated.