Electricity is based on the principle that electrons are attracted to protons. Electron movement can be created when the atomic structure of a material is forced to become imbalanced. Atoms are made up of an equal quantity of positively and negatively charged parts. The nucleus contains protons, with a positive charge, and neutrons with a neutral charge. The negative charge or electrons constantly orbit around the nucleus in valence rings.
If an electron were to be separated from an atom it would assume a net positive charge and become a position ion. On the other hand, if an element were to "acquire" an electron it would have a net negative charge and become a negative ion. If we were to store these positive and negative ions in a container we would have a power source, or battery.
Electricity is the flow of electrons from a greater potential (more electrons) to a lesser potential (less electrons). If a path were provided for the electrons from the negative ions to flow to the positive ions each ion could then maintain its balanced condition. The pressure that the electrons exert when returning to its source is called voltage. When voltage (V) is measured with a voltmeter, the value displayed represents the attractive force, or electromotive force available to get the atoms in balance again.
Amperage is a measure of the actually quantity of electrons that flow from the net negative charge to the net positive charge. This movement of electrons, or current, is what actually does the work in an electrical circuit. Current flow is measured in units of Amperes, or Amps (A). Amperage is a time-based unit. One Amp is equal to 6.28 x 1028 electrons moving past one point in one second. When an ammeter is connected in series with a circuit, the actual quantity of electrons that flow through the circuit are measured.
Resistance is an element’s ability to oppose current flow. The resistance of an element depends upon its atomic structure- specifically how many electrons are held in orbit in the outermost or valence ring. Up to eight electrons can occupy the valence ring of an atom. When fewer electrons are present in the valence ring there is more "room" for electrons to flow across the surface of an atom.
Electrically speaking, elements can be categorized as conductors, insulators and semi-conductors. Conductors are elements with between one and three electrons in their valence ring. Insulators are elements that contain between five and eight valence ring electrons. Semi-conductors are elements that contain four electrons in their valence ring.
Impedance is something that restricts flow. If you put a number of connections along an electrical circuit, each connection becomes a source of resistance slowing the flow of electricity to its final destination. A common analogy would be a coke bottle; if you turn a coke bottle upside down to empty its contents it takes a longer period of time to do so. There is resistance within the bottle to empty a large volume of fluid through a low volume orifice. Now, take the same bottle turned on its side so there is air space present at the mouth of the bottle while pouring out the fluid. The process takes less time due to low impedance (less resistance). The resistance we find in an electrical circuit is measured in Ohms. The resistance of a circuit varies depending on the amount and type of components used in the circuit. When an Ohmmeter is used to measure resistance. Current is applied to the component from a power source (battery) in the meter. The voltage that returns to the meter is converter to a resistive value.
The main factors which determine resistance are the material used, the size and cross section of the wire, the length of the wire and the temperature that these items operate. Some materials have more resistance than others. Those with high resistance are said to be insulators. Rubber materials (or rubber-like plastics) are some of the most common insulators used in vehicles as they have a very high resistance to electricity. Very low resistance materials are said to be conductors. Copper wire is among the best conductors. Most automotive wiring is made of copper. Silver is actually a superior conductor to copper and is used in some relay contacts, but its high cost prohibits its use as common wiring. Airbag systems commonly use gold plated terminal to ensure that current will readily flow through the system. Gold, while cost prohibitive, will not react to air and contaminants that can contribute to unwanted voltage drops.
Larger diameter wires provide more surface area for current flow. The larger the wire size being used, the less resistance the wire will have. Solid conductors provide less surface area when compared to stranded conductors. Stranded conductors have the capacity to carry greater currents when compared to solid conductors of the same gauge (size). This is because the individual strands of a stranded conductor contribute to greater surface area. This is why components which use large amounts of electricity have larger wires supplying current to them. All elements offer some degree of resistance. While copper wire, as an example, is a conductor, it too has a resistive value. For a given thickness of wire, the longer the wire, the greater the resistance. The shorter the wire, the less the resistance. When determining the proper wire for a circuit, both size (gauge) and length must be considered to design a circuit that can handle the current needed to provide enough power to the component being powered. With many materials, the higher the temperature, the greater the resistance (positive temperature coefficient). Some materials exhibit the opposite trait of lower resistance with higher temperatures (negative temperature coefficient). These principles are used in many of the sensors on the engine. As voltage flows through the wiring, these varying properties effect the overall performance of the electrical system, but the current is what actually does the work.
There is a direct relationship between current, voltage and resistance. The relationship between current, voltage and resistance can be summed up by a statement known as Ohm's law.
Voltage (E) is equal to amperage (I) times resistance (R); or,
E=I x R
One volt will push one amp of current through one Ohm of resistance in one second’s time.
Ohm’s law can also be expressed as:
R=E/I or I=E/R
In each of these formulas, "E" is the voltage, "I" represents current (expressed in Amps) and "R" is resistance, expressed in Ohms. A majority of the electrical circuits in an automobile are designed to function at a voltage typically between 13.8 and 14.4 volts. When a stable voltage range is maintained, current flow is regulated by the resistance of the loads in any given circuit. The basic point to remember is that as the resistance of a circuit goes up, the amount of current that flows in the circuit will go down, so long as voltage remains the same.
Wattage
The amount of work that can be performed in an electrical circuit is the product of pressure (voltage) forcing current through a circuit. This combination of amperage and voltage is power. The unit of power is the watt (W). The relationship between power, voltage and current in direct current (DC) circuits is expressed as:
Power (W) is equal to amperage (I) times voltage (E); or,
W=I x E
For as much as power can be an indication of how much work can be performed it is also a requirement. A certain amount of current has to be forced through a component in order for that component to function.