Electric Charge and Electric Force
The study of the electric force will begin with a review of the concept of the electric charge and electrostatics.
Electrostatics is the study of static electric charges and electrical forces (i.e. for charges that are stationary or not in motion). The information derived about the behavior of the electric charge will be used to develop the concepts of electric currents (due to moving charges), the electric circuit, electrical energy and power in another unit yet to be covered.
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Electric Charge
The electric charge is an invisible property acquired by matter that can be observed by the interactions it produces.
All matter (solids, liquids, and gases) are made of atoms.
An atom is composed of electrons, protons and neutrons. The protons and neutrons are tightly bound together to form the nucleus at the center of the atom. The electrons swarm around the nucleus in random directions.
[The strong nuclear force that holds protons and neutrons together inside the nucleus acts only at extremely short distances -- too short to affect these electrons moving around the nucleus].
Electrons have a negative charge while protons have a positive charge.
Neutrons have no electric charge.
The amount of negative charge on an electron is exactly equal to the amount of (opposite) positive charge on a proton.
Since atoms normally have equal numbers of electrons and protons, the total amount of positive charge "balance" the negative charge. Therefore, an atom is described as being electrically neutral, and there is no overall charge on the neutral atom.
Positive and negative charges interact in specific ways.
Charges that are same (or like) repel each other. Charges that are different (or unlike) attract each other.
Protons cannot move easily from one object to another since they are held too tightly within the nucleus of an atom.
Conductors and Insulators
The electrons moving around the nucleus can be moved from an atom to another atom, and from object to object. These electrons will move depending on whether the material is a conductor or an insulator.
Some of the electrons in a conductor are held loosely by the atom. Such electrons move freely from atom to atom within the material.
In insulators, the electrons are held tightly to the atom and are not able to move freely within the material.
Static Electricity or Electrostatic Charge
The stationary electric charge that may accumulate on an object is called an electrostatic charge or static electricity.
Whenever an on object is charged, charges can only be transferred from one object to another. No electrons are created or destroyed. The total amount of charge remains constant. Thus, charge is always conserved!
When an atom gains or loses electrons, it becomes charged and the "charged" atom is called an ion. An atom may gain excess electrons and becomes a negatively charged ion. If the atom loses one or more electrons, it becomes a positively charged ion -- in this case, the charge balance is altered due to the deficiency of electrons.
In solid objects, static charges are due to the gain or loss of electrons only.
Source: http://facstaff.gpc.edu/~pgore/PhysicalScience/electric-charge.html