Current and Resistance

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Current and Resistance
2015-05-06 06:37:08

Fizik II. Vize
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  1. An electric current in a conductor
  2. The SI unit of electric current
    Ampere (1A=1C/s)
  3. The total charge that passes through the plane in time interval 0-t
  4. Charge of an electron
    1 e- = 1.6 x 10-19 C
  5. Direction of current
    • Current and positive charge carriers move in the same direction
    • Actual charge carriers are negative and move in the opposite direction.

    higher potential(+)lower potential (-)
  6. AC - DC
    Alternating Current: Provided by power companies

    Direct Current: Provided by batteries
  7. Current Density
    Vector quantity. Flow of charge through the cross-section of conductor at particular point.

    •  (dot product)
    •  (A/m2)
  8. Direction of current density
    Positive moving charges→Same with their velocity

    Negative moving charges→Opposite of their velocity
  9. Drift speed of the charge carriers
    When an electric field E is established in a conductor, the charge carriers (assumed positive) acquire a drift speed vd in the direction of E.

       (ne=carrier charge density)

  10. The resistance of a conductor
  11. Resistivity of a conductor

    • (σ is the conductivity of the material)
    • (E is the magnitude of of the applied electric field)
  12. The applied electric field
  13. The resistance R of a conducting wire
  14. Change of ρ with temperature
  15. Ohm's Law in a macroscopic view or Resistivity of a metal

    • n: number of free electrons per unit volume
    • : mean time between the collisions of an electron with the atoms of the metal
  16. Power
  17. Resistive Dissipation
    If the device is a resistor, we can write:
    • In a resistor, electric potential energy is converted to internal thermal energy
  18. Semiconductors
    The materials that have a few coduction electrons but can become conductor when they are doped with other atoms that contribute free electrons.
  19. Superconductors
    The materials that lose all electrical resistance at low temperatures.