Electric Charge and the Electrical Structure of Matter

Fundamental Law of Electric Charge: Opposite electric charges attract each other. Similar electric charges repel each other. A Simple Model of the Structure of Matter 1. All matter is composed of sub-microscopic particles, called atoms. 2. Electric charges are carried by particles within each atom that are called electrons and protons. 3. Protons are found in a small central region of the atom, called the nucleus. They are small, heavy particles, and each one carries a positive electric charge of a specific magnitude, called the elementary. 4. Electrons move about in the vast space around this central nucleus. They are small, very light particles, yet each of them carries a negative electric charge equal in magnitude to that of the proton. 5. Atoms are normally electrically neutral, because the number of positive protons in the nucleus is equal to the number of negative electrons moving around the nucleus. 6. Neutrons are small, heavy particles found in the nucleus, and they carry no electric charge. 7. An atom may gain electrons. Then it is no longer neutral, but instead has an excess of electrons and, therefore, a net positive charge. Such an atom is called a negative ion. 8. An atom may also lose electrons. As a result, it will have a deficit of electrons and, therefore, a net positive charge. Such an atom is called a positive ion. All electric charges in solids result from either an excess or a deficit of electrons. Conductor- solids in which electrons are able to move easily from one atom to another. Insulator- solids in which the electrons are not free to move about easily from atom to another. Gazes and liquids can be either conductors or insulators. 15.2 Transfer of Electric Charge Induced Charge Separation The positive charges on a solid conductor are fixed and cannot move. Some negative electrons are quite free to move about from atom to atom. Charging by Contact An object charged by contact has the same sign as the charging rod. Charging by Induction An object that is charged by induction has a charge opposite to that of the carrying rod. 15.3 Electric Forces - Coulomb's Law The magnitude of the electric force is inversely proportional to the square of the distance between the centers of the charged objects. 15.4 Electric Fields Every charged object creates an electric field of force in the space around it. Any other charged object in that space will experience a force of attraction or repulsion from the presence of the electric field