Basic Electrical Engineering
Module 1 – Introduction to Basic Electricity
What is electricity?
The invisible energy that constitutes the flow of
electrons in a closed circuit to do work is called
‘electricity’.
History of Electricity
Long before any knowledge of electricity existed, people were aware of shocks
from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish
as the "Thunderer of the Nile", and described them as the "protectors" of all other
fish. Electric fish were again reported millennia later by ancient
Greek, Roman and Arabic naturalists and physicians.[2] Several ancient writers, such
as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric
shocks delivered by electric catfish and electric rays, and knew that such shocks
could travel along conducting objects.
Ancient cultures around the Mediterranean knew that certain
objects, such as rods of amber, could be rubbed with cat's fur
to attract light objects like feathers. Thales of Miletus made a
series of observations on static electricity around 600 BCE
Electricity would remain little more than an intellectual
curiosity for millennia until 1600, when the English
scientist William Gilbert wrote De Magnete, in which he made a careful study of
electricity and magnetism, distinguishing the lodestone effect from static electricity
produced by rubbing amber.[6] He coined the New Latin word electricus ("of amber"
or "like amber", from ἤλεκτρον, elektron, the Greek word for "amber") to refer to
the property of attracting small objects after being rubbed.[11] This association gave
rise to the English words "electric" and "electricity", which made their first
appearance in print in Thomas Browne's Pseudodoxia Epidemica of 1646.
Later in the 18th century, Benjamin Franklin conducted
extensive research in electricity, selling his possessions to
fund his work. In June 1752 he is reputed to have attached
a metal key to the bottom of a dampened kite string and
flown the kite in a storm-threatened sky.[14] A succession
of sparks jumping from the key to the back of his hand
showed that lightning was indeed electrical in nature. He
also explained the apparently paradoxical behavior of
the Leyden jar as a device for storing large amounts of
electrical charge in terms of electricity consisting of both
positive and negative charges.[13]
While the early 19th century had seen rapid progress in electrical science, the late
19th century would see the greatest progress in electrical engineering. Through such
people as Alexander Graham Bell, Ottó Bláthy, Thomas Edison, Galileo
Ferraris, Oliver Heaviside, Ányos Jedlik, William Thomson, 1st Baron Kelvin, Charles
Algernon Parsons, Werner von Siemens, Joseph Swan, Reginald Fessenden, Nikola
Tesla and George Westinghouse, electricity turned from a scientific curiosity into an
essential tool for modern life.
Modern Electron Theory
According to modern electron theory, every matter (whether solid, liquid, or gas)
consists of tiny divisible particles called ‘molecules’. A molecule is further made up
of very minute particles called ‘atoms’; and all atoms consist of electrons, protons,
and neutrons.
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Atomic Number
All elements are arranged in the periodic table of the elements in order according to
their atomic number. The atomic number equals the number of protons in the
nucleus. For example, hydrogen has an atomic number of 1 and helium has an
atomic number of 2. In their normal (or neutral) state, all atoms of a given element
have the same number of electrons as protons; the positive charges cancel the
negative charges, and the atom has a net charge of zero, making it electrically
balanced.
Shells, Orbits, and Energy Levels
According to the classic Bohr model, an atom is visualized as having a planetary type
of structure that consists of a central nucleus surrounded by orbiting electrons, as
illustrated in Figure 1. The nucleus consists of positively charged particles called
protons and uncharged particles called neutrons. The basic particles of negative
charge are called electrons, which orbit the nucleus. Each type of atom has a certain
number of protons that distinguishes it from the atoms of all other elements.
As you have seen in the Bohr model, electrons orbit the nucleus of an atom at
certain distances from the nucleus and are restricted to these specific orbits. Each
orbit corresponds to a different energy level within the atom known as a shell. The
shells are designated 1, 2, 3, and so on, with 1 being closest to the nucleus. Electrons
further from the nucleus are at higher energy levels.
Valence Electrons
Electrons that are in orbits farther from the nucleus have higher energy and are less
tightly bound to the atom than those closer to the nucleus. This is because the force
of attraction between the positively charged nucleus and the negatively charged
electron decreases with increasing distance from the nucleus. Electrons with the
highest energy levels exist in the outermost shell of an atom and are relatively
loosely bound to the atom. This outermost shell is known as the valence shell, and
electrons in this shell are called valence electrons.
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Energy Levels and Ionization Energy
Categories of Materials
If an electron absorbs a photon with sufficient energy, it escapes from the atom and
becomes a free electron. This is indicated by the ionization energy level in Figure 3.
Any time an atom or group of atoms is left with a net charge, it is called an ion.
When an electron escapes from the neutral hydrogen atom (designated H), the atom
is left with a net positive charge and becomes a positive ion (designated H+). In other
cases, an atom or group of atoms can acquire an electron, in which case it is called a
negative ion.
Conductors are materials that readily allow current. They have a large
number of free electrons and are characterized by one to three valence electrons in
their structure. Most metals are good conductors.
The Copper Atom
The copper atom has 29 electrons that orbit the nucleus in four shells. The number
of electrons in each shell follows a predictable pattern according to the formula,
2N^2 where N is the number of the shell. The first shell of any atom can have up to
two electrons, the second shell up to eight electrons, the third shell up to 18
electrons, and the fourth shell up to 32 electrons.
Semiconductors are classed below the conductors in their ability to
carry current because they have fewer free electrons than do conductors.
Semiconductors have four valence electrons in their atomic structures.
Insulators are nonmetallic materials that are poor conductors of electric current;
they are used to prevent current where it is not wanted. Insulators have no free
electrons in their structure.
SECTION 1
CHECKUP
1. What is the basic particle of negative charge?
2. Define atom.
3. What does an atom consist of?
4. Define atomic number.
5. Do all elements have the same types of atoms?
6. What is a free electron?
7. What is a shell in the atomic structure?
8. Name two conductive materials.
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