Basic Concepts of Electricity

• Certain types of materials mysteriously attract one another after being rubbed together, and there is an attractive force that can be demonstrated even when the two materials are separated
• Identical materials, after being rubbed with their respective cloths, always repel each other
• In the old days, it was found that any material demonstrating properties of attraction or repulsion when rubbed could be classed into one of two categories:

  • attracted to glass and repelled by wax
  • repelled by glass and attracted to wax

  there were no materials found that would be attracted to or repelled by both or that reacted to one and not the other
• What did Charles Defay demonstrate?

  there were two different types of change wrought by rubbing certain materials together: attraction and repulsion

  the "fluid transfer" between objects was known as charge
• Franklin's theory

  wool removed some of the fluid (charge) from the wax, causing an excess of fluid on the wool and a deficiency on the wax

  this disparity in fluid content causes an attractive force, as the fluid tries to regain its former balance

  as a result, the type of change associated with wax became negative (deficiency) while the charge associated with wool was positive (excess)
• What did Charles Coulomb do?

  used a torsional balance to measure the force generated between two electrically charged objects; this led to the development of the coulomb
• Coulomb

  one electron has a charge of 1.6 x 10 ^ -19 coulombs
• elementary charge

  the last figure of charge for the electron
• It was discovered that the "fluid" on wax was composed of small bits of matter called electrons
• What happens if you change the number of protons in an atom's nucleus?

  you change the type of atom it is
• What happens if neutrons are added or gained?

  the atom has the same chemical identity, but its mass changes, and it may acquire nuclear properties like radioactivity
• The attraction of protons and electrons over a distance causes the attraction between rubbed objects, where electrons are moved away from their original atoms to reside around atoms of another object
• Strong Nuclear Force

  the only reason protons bind together in the nucleus of an atom; has effect only under very short distances
• What happens if the number of electrons is changed?

  the atom's net electric charge will be imbalanced
• What happens when certain combinations of materials are rubbed together?

  electrons from the atoms of one material are forced by the rubbing to leave their respective atoms and transfer over to the atoms of the other material
• Static Electricity

  the result of an imbalance of the fluid between objects

  called static because the displaced electrons tend to remain stationary after being moved from one insulating material to another
• Negatively charged vs. Positively charged atom

  negatively charged: an object whose atoms have received a surplus of electrons

  positively charged: an object with missing electrons
• What did Michael Faraday prove?

  static electricity was the same as that produced by a battery or generator
• Free Electrons

  electrons that are free to leave their respective atoms and float around in the space between adjacent atoms
• Electric conductivity:

  relative mobility of electrons within a material
• What is conductivity determined by?

  the types of atoms in a material and how the atoms are linked together with one another
• Conductors vs. Insulators

  conductors: materials with high electron mobility (many free electrons)

  insulators: materials with low electron mobility (few or no free electrons)
• Do all conductors/insulators have the same level of conductivity?

  No
• Electric Current:

  the uniform motion of electrons

  also called electricity or dynamic electricity
• Process of uniform electron motion

  As each electron moves uniformly through a conductor, it pushes on the one ahead of it, such that all the electrons move together as a group

  The starting and stopping of electron flow through the length of a conductive path is virtually instantaneous from one end of a conductor to the other, even though the motion of each electron may be very slow
• What is the speed of light?

  the overall effect from one end of a conductor to another; 186 k mi/sec
• If we want electrons to flow in a certain direction to a certain place, we must use a wire to provide the proper path for movement
• The continuous flow of electrons requires there to be an unbroken path to permit that flow; air breaks electrical continuity
• circuit

  a never-ending looped pathway for electrons
• Why do we need an imbalance of electric charge to produce a force to push electrons through a circuit?

  an imbalance manifests as an attractive force between two objects; if a conductive wire is placed between two charged objects, electrons will flow through the wire, as excess electrons in one rush to fill a deficiency in another
• The attractive force provokes electrons to flow in a uniform direction through the wire, until the charge in that area neutralizes and the force between two objects diminishes
• When electrons are poised in a static condition, the energy stored there is called potential energy because it has the possibility of release that hasn't been fully realized
• voltage

  measure of P.E. per unit charge of electrons; specific potential energy

  always referenced between two points
• Any source of voltage, including batteries, have two points for electrical contact (point 1 and 2)

  • horizontal lines of varying length indicate that this is a battery and which direction the battery's voltage will try to push electrons through a circuit
  • the negative end of the battery always has the shortest dash, and the positive end has the longest dash
• So long as the battery continues to produce voltage and the continuity of the electrical path isn't broken, electrons will continue to flow in the circuit
• Direct current, DC

  single-direction flow of electrons; so long as the voltage source keeps "pushing" in the same direction, the electron flow will continue to move in the same direction in the circuit
• Since a current is composed of individual electrons flowing in unison through a conductor, the amount of flow throughout a single circuit will be the same at any point
• What happens if we break the circuit's continuity at any point?

  the electric current will cease in the entire loop, and the full voltage produced by the battery will be manifested across the break, between wire ends that used to be connected
• Resistance

  opposition to electric current; depends on type of material, its cross-sectional area, and its temperature

  conductors have low resistance; insulators have high resistance
• Friction

  occurs when electrons move against the opposition of resistance; manifests in the form of heat