ELECTRIC CHARGE

• Four Distinct Classes of Fundamental Forces

   

  1.    Gravitational interaction

  2.    Electromagnetic interaction

  3.    Strong interaction

  4.    Weak interaction
• Electric Charge

  -       The ancient Greeks discovered as early as 600 B.C. that after they rubbed amber with wool, the amber could attract other objects. Today we say that the amber has acquired a net electric charge, or has become charged. The word "electric" is derived from the Greek word elektron, meaning amber. When you scuff your shoes across a nylon carpet, you become electrically charged, and you can charge a comb by passing it through dry hair.
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  Plastic rods and fur (real or fake) are particularly good for demonstrating electrostatics, interactions the between electric charges that are at rest (or nearly so). After we charge both plastic rods in Figure 2a by rubbing them with the piece of fur, we find that the rods repel each other.
• Electric Charge and the Structure of Matter

  -       The proton and neutron are combinations of other entities called quarks, which have charges of +1/3 and + 2/3 times the electron charge. Isolated quarks have not been observed, and there are theoretical reasons to believe that it is impossible in principle to observe a quark in isolation.
• The protons and neutrons in an atom make up a small, very dense core called the nucleus, with dimensions of the order of 10-15 m.
• Surrounding the nucleus are the electrons, extending out to distances of the order of 10-10 from the nucleus
• The number of protons or electrons in a neutral atom of an element is called the atomic number of the element
• If one or more electrons are removed from an atom, what remains is called a positive ion
• A negative ion is an atom that has gained one or more electrons
• This gain or loss of electrons is called ionization
• Charging by Induction

  -       We can charge a metal ball using a copper wire and an electrically charged plastic rod.

  -       In this process, some of the excess electrons on the rod are transferred from it to the ball, leaving the rod with a smaller negative charge. But there is a different technique in which the plastic rod can give another body a charge of opposite sign without losing any of its own charge. This process is called charging by induction.