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Explaining Static Electricity

Key definitions

  • Neutral is having no overall positive or negative charge.

Friction and charging

  • The force of friction causes charging.
    • As mentioned before, when rubbing a polythene rod with a cloth, friction transfers electrons from one material to the other. In this case, polythene receives the electrons from the cloth.
  • Electrons are a part of every atom. They are negatively charged, and they are found on the outside of the atom.
  • The nucleus in the center of an atom has a positive charge due to protons.
  • The positive and negative charges in an atom are equal. Therefore, there is no electric charge. The atom is neutral.
    • Neutral means having no overall positive or negative charge.
  • Since the outer electrons are relatively weakly held in the atom, they can be pulled away by the force of friction.
    • When an atom has lost an electron, it becomes positively charged (because there will be more protons than electrons).
  • Charge is always the result of gaining or losing electrons. Positive charge is NOT transferred.
    • An object which gains electrons becomes negative.
    • An object which loses electrons becomes positive.

Conductors and insulators

  • An electrical conductor is a substance that allows the flow of electrons (electric current).
    • Metals are electrical conductors. Since electrons flow through them, the metal doesn’t stay charged.
  • An electrical insulator is a substance that inhibits the flow of electrons (electric current).
  • In insulators, the electrons are tightly bound to their atoms and not easily removed.
  • In conductors, some of the electrons are free to move between atoms.
    • These electrons are sometimes referred to as free electrons.
  • When rubbing a polythene rod:
    • it gains electrons from the cloth and the rod becomes negatively charged
    • electrons can’t move through the polythene, so the end which was rubbed remains charged
  • When rubbing a copper rod:
    • electrons are also transferred by friction, but the electrons are free to move, so they flow through the rod, through your hand, and into the Earth
    • therefore, the copper rod remains uncharged
  • A metal object can be charged if it is held by an insulating handle.
    • In this case, the charge will spread evenly through the conductor.