Phy Chapter 7 Electrostatics Caltec S.4

ELECTROSTATICS Electrostatics is simply the study of electric charges at rest. The structure of an Atom A substance is made up of tiny atoms which consist of electrons, protons and neutrons. The electrons are found in the shell while protons and neutrons are found in the nucleus, the central part of the atom. An electron carries a negative charge while a proton carries a positive charge. The magnitude of the negative charge on an electron and positive charge on a proton are equal. The number of electrons and protons in an atom is always equal, thus the atom is electrically neutral. Conductors and insulators A conductor is a substance which has atoms in which electrons can move from one part of the conductor to another. These electrons are called free electrons i.e. electrons are loosely bound to atoms. Electrons therefore are able to transfer charges from one part of a conductor to another. The transfer of charge in this way is called conduction. Examples are any metal such as copper, aluminum, brass and electrolytes. An insulator is a substance which has its electrons tightly bound to the atoms, that is, the electrons are not free to move about. Insulators are therefore poor conductors. Examples are glass, fur, silk, ebonite, polythene etc. Charging an Insulator by friction When glass and silk are rubbed together, glass atoms tend to lose electrons faster than the atoms of silk. The electrons lost by the atoms of glass are acquired by the atoms of silk. The exchange of electrons makes the atoms of glass to have more protons than electrons and the atoms of silk to have more electrons than protons. Thus glass and silk become positively and negatively charged respectively. Note! In all cases, a substance is charged when it has more protons than …