Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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Electrical Fundamentals 49
SUMMARY
A conductor is a metallic element that contains
fewer than four electrons in its outer shell. An
insulator is a non-metallic substance that contains
more than four electrons in the outer shell.
Semiconductors are a group of materials that
cannot be classified either as conductors or
insulators; they have exactly four electrons in their
outer shell. Current flow is measured by the number
of free electrons passing a given point in an
electrical circuit per second. Electrical pressure or
charge differential is measured in volts, resistance
in ohms and current in amperes. If a hydraulic circuit
analogy is used to describe an electrical circuit,
voltage is equivalent to fluid pressure,
current to the flow in gpm, and resistance to flow
restriction.
Capacitors are used to store electrons: this consists
of conductor plates separated by a dielectric.
Capacitance is measured in farads: capacitors are
rated by voltage and by capacitance.