What is commonly defined as electricity is really just the movement of electrons. So, lets start at that point.
Current (I, Amps)
Current (as the name implies) is the movement or flow of electrons (I) and is measured in units of Amperes. This is usually abbreviated to Amp or, even shorter, A. The flow of electrons in an electrical current can be considered the same as the flow of water molecules in a stream.
To get anything to move requires potential and the same thing happens
Potential (V, Volts)
Potential is the force (called Electromotive Force or EMF) that drives the electrons and has a measurement of voltage. This is abbreviated as a unit of measurement to Volt or even further to V.
Resistance (R, Ohms)
Resistance is the property that resists current flow. It is analogous to friction in mechanical systems. The unit of this is ohm (we have to give some credit to the fellow who first named it). It is sometimes shown with its official ohm mark (Ω) and the short form of the word resistance is always R.
Resistance not only depends on the material used for the conductor but also upon size and temperature. Increase in the cross-sectional area will decrease the resistance Increase in the length will increase the resistance. Increase in the temperature will increase the resistance (for most materials that conduct electricity)
Capacitance (C, Farads)
Any two conductors separated by an insulating material form a capacitor or condenser. Capacitance of a device is its capacity to hold electrons or a charge. The units of measurement are farads. We commonly see it in smaller amounts called microfarads μF and picofarads pF. Capacitance depends on the construction.
Magnetic Flux (Unit of Measurement is Webers)
When current flows in a conductor, a magnetic field is created around that conductor. This field is commonly presented as lines of magnetic force and magnetic flux refers to the term of measurement of the magnetic flow within the field.
This is comparable to the term current and electron flow in an electric field. The following illustration shows the direction of magnetic flux around a conductor and the application of the easily remembered right-hand-rule. Mentally, place your right hand around the conductor with the thumb pointing in the direction of current flow and the fingers will curl in the direction of magnetic flux.
Magnetic Lines of Force (MMF)
Lines of magnetic force (MMF) have an effect on adjacent conductors and even itself. This effect is most pronounced if the conductor overlaps itself as in the shape of a coil.
Any current-carrying conductor that is coiled in this fashion forms an Inductor, named by the way it induces current flow in itself (selfinductance) or in other conductors.
Inductance (L, Henrys)
Opposition to current flowing through an inductor is inductance. This is a circuit property just as resistance is for a resistor. The inductance is in opposition to any change in the current flow. The unit of inductance is Henry (H) and the symbol is L.
Frequency (f, Hertz)
Any electrical system can be placed in one of two categories direct current (dc) or alternating current (dc). In dc systems the current only flows in one direction.
The source of energy maintains a constant electromotive force, as typical with a battery. The majority of electrical systems are ac.
Frequency is the rate of alternating the direction of current flow. The short form is f and units are cycles per second or Hertz (short-formed to Hz).
Reactance (X, Ohms)
The opposition to alternating current (ac) flow in capacitors and inductors is known as reactance. The symbol for capacitive reactance is XC and for inductive reactance XL.
Although we will not go into the derivation of the values, it can be shown that when f is the frequency of the ac current:
XL= 2 Πf L
Impedance (Z, Ohms)
The total opposition or combined impeding effect of resistance plus reactance to the flow of alternating current is impedance. The word impedance is short formed to Z and the unit is ohms.
Active Power (P Watts)
Instead of working directly with the term electrical energy, it is normal practice to use the rate at which energy is utilized during a certain time period. This is defined as power. There are three components of power: active, reactive and apparent.
Active power or real power is the rate at which energy is consumed resulting in useful work being done. For example, when current flows through a resistance, heat is given off. It is given the symbol P and has the units of Watts.
Reactive Power (Q, Vars)
Reactive power is the power produced by current flowing through reactive elements, whether inductance or capacitance. It is given the representative letter Q and has the units volt-amp-reactive (VAR).
Reactive power can also be considered as the rate of exchange of energy between a capacitor or inductor load and a generator or between capacitors and inductors.
Although it does not produce any real work, it is the necessary force acting in generators, motors and transformers. Examples of this are the charging/discharging of a capacitor or coil. Although this creates a transfer of energy, it does not consume or use power as a resistor would.
Apparent Power (U, Volt Amps)
Apparent power is the total or combined power produced by current flowing through any combination of passive and reactive elements. It is given the representative letter U and has the units’ volt-amps (VA).
Power Factor (PF)
Real power/ apparent power
Power Factor is the comparison of Real power to apparent power.
• For a resistor, there is no reactive power consumed. Thus apparent power used is totally real. The power factor would be 1 or often referred to as unity power factor
• For a pure inductor or capacitor, the apparent power consumed is entirely reactive (real power is nil). The power factor would then be 0.
• For power consumed by impedance consisting of resistance, inductance and capacitance the power factor will of course vary between these two limits. The most efficient use or consumption of power is obtained as we approach unity power factor.