Ohm's Law - Ford Ranger Maintaince And Repair Manual

electrons will split off the atom and look for another atom to balance out. If this imbalance is kept up,
electrons will continue to move and an electrical flow will exist.
Many people have been taught electrical theory using an analogy with water. In a comparison with water
flowing through a pipe, the electrons would be the water and the wire is the pipe.
The flow of electricity can be measured much like the flow of water through a pipe. The unit of measurement
used is amperes, frequently abbreviated as amps (a). You can compare amperage to the volume of water
flowing through a pipe. When connected to a circuit, an ammeter will measure the actual amount of current
flowing through the circuit. When relatively few electrons flow through a circuit, the amperage is low. When
many electrons flow, the amperage is high.
Water pressure is measured in units such as pounds per square inch (psi); The electrical pressure is measured
in units called volts (v). When a voltmeter is connected to a circuit, it is measuring the electrical pressure.
The actual flow of electricity depends not only on voltage and amperage, but also on the resistance of the
circuit. The higher the resistance, the higher the force necessary to push the current through the circuit. The
standard unit for measuring resistance is an ohm. Resistance in a circuit varies depending on the amount and
type of components used in the circuit. The main factors which determine resistance are:
• Material−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. 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. Most
automotive wiring is made of copper.
• Size−the larger the wire size being used, the less resistance the wire will have. This is why
components which use large amounts of electricity usually have large wires supplying current to
them.
• Length−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 and length must
be considered to design a circuit that can handle the current needs of the component.
Temperature−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.

OHM'S LAW

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): E=I x R
Other forms of the formula are R=E/I and I=E/R
In each of these formulas, E is the voltage in volts, I is the current in amps and R is the resistance in ohms.
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, if voltage remains the same.
The amount of work that the electricity can perform is expressed as power. The unit of power is the watt (w).
The relationship between power, voltage and current is expressed as:
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HOW DOES ELECTRICITY WORK: THE WATER ANALOGY