The First Law of Electrostatics

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

Figure 4 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.

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ATOM AND ITS FORCES Basic Electrical Theory

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,

Figure 5 Electrostatic Field Between Two Charges of Opposite Polarity

as shown in Figure 6.

Figure 6 Electrostatic Field Between Two Charges of Like Polarity

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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.

F K (1-1)

q1 q2

d2

where

F = force of electrostatic attraction or prepulsion (Newtons)

K = constant of proportionality (Coulomb 2/N-m2)

q1 = charge of first particle (Coulombs)

q2 = charge of second particle (Coulombs)

d = distance between two particles (Meters)

If q1 and q2 are both either

Figure 7 Potential Difference Between Two Charged Objects

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 term

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.

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ATOM AND ITS FORCES Basic Electrical Theory

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 pull

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.