What is electricity? Electricity is defined as “the flow of electrons
through simple materials and devices” or “that force which moves
electrons.” Scientists think electricity is produced by very tiny
particles called electrons and protons. These particles are too small to
be seen, but exist as subatomic particles in the atom. To understand
how they exist, you must first understand the structure of the atom
charge (+) of electricity and is located in
the nucleus. The number of protons in
the nucleus of any atom specifies the
atomic number of that atom or of that
element. For example, the carbon atom
contains six protons in its nucleus;
therefore, the atomic number for carbon is
six, as shown in Figure 2.
In its natural state, an atom of any
element contains an equal number of
electrons and protons. The negative
charge (-) of each electron is equal in
magnitude to the positive charge (+) of
each proton; therefore, the two opposite
charges cancel, and the atom is said to be
electrically neutral, or in balance.
attraction is called electrostatic force, the force that holds the electron in orbit. This force may
be illustrated with lines as shown in Figure 3.
Without this electrostatic force, the electron, which is traveling at high speed, could not stay in
its orbit. Bodies that attract each other in this way are called charged bodies. As mentioned
previously, the electron has a negative charge, and the nucleus (due to the proton) has a positive
charge.
These charges are referred to as electrostatic charges. In nature, unlike charges (like electrons
and protons) attract each other, and like charges repel each other. These facts are known as the
First Law of Electrostatics and are sometimes referred to as the law of electrical charges. This
law should be remembered because it is one of the vital concepts in electricity.
Some atoms can lose electrons and others can gain electrons; thus, it is possible to transfer
electrons from one object to another. When this occurs, the equal distribution of negative and
positive charges no longer exists. One object will contain an excess of electrons and become
negatively charged, and the other will become deficient in electrons and become positively
charged. These objects, which can contain billions of atoms, will then follow the same law of
electrostatics as the electron and proton example shown above. The electrons that can move
around within an object are said to be free electrons and will be discussed in more detail in a
later section. The greater the number of these free electrons an object contains, the greater its
negative electric charge. Thus, the electric charge can be used as a measure of electrons.
Electrostatic Field
A special force is acting between
the charged objects discussed
above. Forces of this type are the
result of an electrostatic field that
exists around each charged particle
or object. This electrostatic field,
and the force it creates, can be
illustrated with lines called “lines
of force” as shown in Figure 4.
Charged objects repel or attract each other because of the way these fields act together. This
force is present with every charged object. When two objects of opposite charge are brought
near one another, the electrostatic field is concentrated in the area between them, as shown in
Figure 5. The direction of the small arrows shows the direction of the force as it would act upon
an electron if it were released into the electric field.
When two objects of like charge are brought near one another, the lines of force repel each other,
as shown in Figure 6.
The strength of the attraction or of the repulsion force depends upon two factors: (1) the amount
of charge on each object, and (2) the distance between the objects. The greater the charge on
the objects, the greater the electrostatic field. The greater the distance between the objects, the
weaker the electrostatic field between them, and vice versa. This leads us to the law of
electrostatic attraction, commonly referred to as Coulomb’s Law of electrostatic charges, which
states that the force of electrostatic attraction, or repulsion, is directly proportional to the product
of the two charges and inversely proportional to the square of the distance between them as
shown in Equation 1-1.
If q1 and q2 are both either
positively or negatively
charged, the force is repulsive.
If q1 and q2 are opposite
polarity or charge, the force is
attractive.
used to describe how large the
electrostatic force is between
two charged objects. If a
charged body is placed
between two objects with a
potential difference, the
charged body will try to move
in one direction, depending
upon the polarity of the object. If an electron is placed between a negatively-charged body and
a positively-charged body, the action due to the potential difference is to push the electron toward
the positively-charged object. The electron, being negatively charged, will be repelled from the
negatively-charged object and attracted by the positively-charged object, as shown in Figure 7.
Due to the force of its electrostatic field, these electrical charges have the ability to do work by
moving another charged particle by attraction and/or repulsion. This ability to do work is called
“potential”; therefore, if one charge is different from another, there is a potential difference
between them. The sum of the potential differences of all charged particles in the electrostatic
field is referred to as electromotive force (EMF).
The basic unit of measure of potential difference is the “volt.” The symbol for potential
difference is “V,” indicating the ability to do the work of forcing electrons to move. Because
the volt unit is used, potential difference is also called “voltage.” The unit volt will be covered
in greater detail in the next chapter.
the nucleus and the electron together, the electron is in motion and trying to pull away. These
two effects balance, keeping the electron in orbit. The electrons in an atom exist in different
energy levels. The energy level of an electron is proportional to its distance from the nucleus.
Higher energy level electrons exist in orbits, or shells, that are farther away from the nucleus.
These shells nest inside one another and surround the nucleus. The nucleus is the center of all
the shells. The shells are lettered beginning with the shell nearest the nucleus: K, L, M, N, O,
P, and Q. Each shell has a maximum number of electrons it can hold. For example, the K shell
will hold a maximum of two electrons and the L shell will hold a maximum of eight electrons.
As shown in Figure 8, each shell has a specific number of electrons that it will hold for a
particular atom.
There are two simple rules concerning electron shells that make it possible to predict the electron
distribution of any element:
1.The maximum number of electrons that can fit in the outermost shell of any atom is
8.
2. The maximum number of electrons that can fit in the next-to-outermost shell of any atom
is 18.
An important point to remember is that when the outer shell of an atom contains eight electrons,
the atom becomes very stable, or very resistant to changes in its structure. This also means that
atoms with one or two electrons in their outer shell can lose electrons much more easily than atoms
with full outer shells. The electrons in the outermost shell are called valence electrons. When
external energy, such as heat, light, or electrical energy, is applied to certain materials, the
electrons gain energy, become excited, and may move to a higher energy level. If enough energy is
applied to the atom, some of thevalence electrons will leave the atom. These electrons are called
free electrons. It is the movement of free electrons that provides electric current in a metal
conductor. An atom that has lost or gained one or more electrons is said to be ionized or to have
an ion change. If the atom loses one or more electrons, it becomes positively charged and is
referred to as a positive ion. If an atom gains one or more electrons, it becomes
negatively charged and is referred to as a negative ion.
The Atom
Elements are the basic building
blocks of all matter. The atom is
the smallest particle to which an
element can be reduced while still
keeping the properties of that
element. An atom consists of a
positively charged nucleus
surrounded by negatively charged
electrons, so that the atom as a
whole is electrically neutral. The
nucleus is composed of two kinds
of subatomic particles, protons and
neutrons, as shown in Figure 1.
The proton carries a single unit
positive charge equal in magnitude
to the electron charge. The
neutron is slighty heavier than the
proton and is electrically neutral,
as the name implies. These two
particles exist in various combinations, depending upon the element involved. The electron is
blocks of all matter. The atom is
the smallest particle to which an
element can be reduced while still
keeping the properties of that
element. An atom consists of a
positively charged nucleus
surrounded by negatively charged
electrons, so that the atom as a
whole is electrically neutral. The
nucleus is composed of two kinds
of subatomic particles, protons and
neutrons, as shown in Figure 1.
The proton carries a single unit
positive charge equal in magnitude
to the electron charge. The
neutron is slighty heavier than the
proton and is electrically neutral,
as the name implies. These two
particles exist in various combinations, depending upon the element involved. The electron is
the fundamental negative charge (-) of electricity and revolves around the nucleus, or center, of
the atom in concentric orbits, or shells.
The proton is the fundamental positivethe atom in concentric orbits, or shells.
charge (+) of electricity and is located in
the nucleus. The number of protons in
the nucleus of any atom specifies the
atomic number of that atom or of that
element. For example, the carbon atom
contains six protons in its nucleus;
therefore, the atomic number for carbon is
six, as shown in Figure 2.
In its natural state, an atom of any
element contains an equal number of
electrons and protons. The negative
charge (-) of each electron is equal in
magnitude to the positive charge (+) of
each proton; therefore, the two opposite
charges cancel, and the atom is said to be
electrically neutral, or in balance.
Electrostatic Force
One of the mysteries of the atom is that the electron and the nucleus attract each other. Thisattraction is called electrostatic force, the force that holds the electron in orbit. This force may
be illustrated with lines as shown in Figure 3.
Without this electrostatic force, the electron, which is traveling at high speed, could not stay in
its orbit. Bodies that attract each other in this way are called charged bodies. As mentioned
previously, the electron has a negative charge, and the nucleus (due to the proton) has a positive
charge.
The First Law of Electrostatics
The negative charge of the electron is equal, but opposite to, the positive charge of the proton.These charges are referred to as electrostatic charges. In nature, unlike charges (like electrons
and protons) attract each other, and like charges repel each other. These facts are known as the
First Law of Electrostatics and are sometimes referred to as the law of electrical charges. This
law should be remembered because it is one of the vital concepts in electricity.
Some atoms can lose electrons and others can gain electrons; thus, it is possible to transfer
electrons from one object to another. When this occurs, the equal distribution of negative and
positive charges no longer exists. One object will contain an excess of electrons and become
negatively charged, and the other will become deficient in electrons and become positively
charged. These objects, which can contain billions of atoms, will then follow the same law of
electrostatics as the electron and proton example shown above. The electrons that can move
around within an object are said to be free electrons and will be discussed in more detail in a
later section. The greater the number of these free electrons an object contains, the greater its
negative electric charge. Thus, the electric charge can be used as a measure of electrons.
Electrostatic Field
A special force is acting between
the charged objects discussed
above. Forces of this type are the
result of an electrostatic field that
exists around each charged particle
or object. This electrostatic field,
and the force it creates, can be
illustrated with lines called “lines
of force” as shown in Figure 4.
Charged objects repel or attract each other because of the way these fields act together. This
force is present with every charged object. When two objects of opposite charge are brought
near one another, the electrostatic field is concentrated in the area between them, as shown in
Figure 5. The direction of the small arrows shows the direction of the force as it would act upon
an electron if it were released into the electric field.
When two objects of like charge are brought near one another, the lines of force repel each other,
as shown in Figure 6.
The strength of the attraction or of the repulsion force depends upon two factors: (1) the amount
of charge on each object, and (2) the distance between the objects. The greater the charge on
the objects, the greater the electrostatic field. The greater the distance between the objects, the
weaker the electrostatic field between them, and vice versa. This leads us to the law of
electrostatic attraction, commonly referred to as Coulomb’s Law of electrostatic charges, which
states that the force of electrostatic attraction, or repulsion, is directly proportional to the product
of the two charges and inversely proportional to the square of the distance between them as
shown in Equation 1-1.
If q1 and q2 are both either
positively or negatively
charged, the force is repulsive.
If q1 and q2 are opposite
polarity or charge, the force is
attractive.
Potential Difference
Potential difference is the termused to describe how large the
electrostatic force is between
two charged objects. If a
charged body is placed
between two objects with a
potential difference, the
charged body will try to move
in one direction, depending
upon the polarity of the object. If an electron is placed between a negatively-charged body and
a positively-charged body, the action due to the potential difference is to push the electron toward
the positively-charged object. The electron, being negatively charged, will be repelled from the
negatively-charged object and attracted by the positively-charged object, as shown in Figure 7.
Due to the force of its electrostatic field, these electrical charges have the ability to do work by
moving another charged particle by attraction and/or repulsion. This ability to do work is called
“potential”; therefore, if one charge is different from another, there is a potential difference
between them. The sum of the potential differences of all charged particles in the electrostatic
field is referred to as electromotive force (EMF).
The basic unit of measure of potential difference is the “volt.” The symbol for potential
difference is “V,” indicating the ability to do the work of forcing electrons to move. Because
the volt unit is used, potential difference is also called “voltage.” The unit volt will be covered
in greater detail in the next chapter.
Free Electrons
Electrons are in rapid motion around the nucleus. While the electrostatic force is trying to pullthe nucleus and the electron together, the electron is in motion and trying to pull away. These
two effects balance, keeping the electron in orbit. The electrons in an atom exist in different
energy levels. The energy level of an electron is proportional to its distance from the nucleus.
Higher energy level electrons exist in orbits, or shells, that are farther away from the nucleus.
These shells nest inside one another and surround the nucleus. The nucleus is the center of all
the shells. The shells are lettered beginning with the shell nearest the nucleus: K, L, M, N, O,
P, and Q. Each shell has a maximum number of electrons it can hold. For example, the K shell
will hold a maximum of two electrons and the L shell will hold a maximum of eight electrons.
As shown in Figure 8, each shell has a specific number of electrons that it will hold for a
particular atom.
There are two simple rules concerning electron shells that make it possible to predict the electron
distribution of any element:
1.The maximum number of electrons that can fit in the outermost shell of any atom is
8.
2. The maximum number of electrons that can fit in the next-to-outermost shell of any atom
is 18.
An important point to remember is that when the outer shell of an atom contains eight electrons,
the atom becomes very stable, or very resistant to changes in its structure. This also means that
atoms with one or two electrons in their outer shell can lose electrons much more easily than atoms
with full outer shells. The electrons in the outermost shell are called valence electrons. When
external energy, such as heat, light, or electrical energy, is applied to certain materials, the
electrons gain energy, become excited, and may move to a higher energy level. If enough energy is
applied to the atom, some of thevalence electrons will leave the atom. These electrons are called
free electrons. It is the movement of free electrons that provides electric current in a metal
conductor. An atom that has lost or gained one or more electrons is said to be ionized or to have
an ion change. If the atom loses one or more electrons, it becomes positively charged and is
referred to as a positive ion. If an atom gains one or more electrons, it becomes
negatively charged and is referred to as a negative ion.
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