Points to Remember
  1. In metals, the charge carriers constituting current are free electrons.
  2. In liquids, the charge carriers are positive and negative ions.
  3. In gases, the charge carriers are positive ions and free electrons.
  4. In semiconductors, the charge carriers are holes and free electrons.
  5. The conventional direction of the flow of current is opposite to the direction of the flow of electrons.
  6. Current is a scalar quantity.
  7. Current density is a vector quantity.
  8. The direction of current density j is the same as that of electric field E.
  9. Reciprocal of the slope of the V – I graph is equal to the resistance.
  10. The resistance of the conductor depends on the material of the conductor, shape, and size of the conductor as well as on the physical state (Temperature) of the conductor.
  11. Reciprocal of resistance is called conductance, g = 1 / R
  12. While calculating the resistance of a wire by the  formula  R = ρ*L / A
  13. If two resistances R1 and R2 are in parallel, then the currents I1 and I2 in them will be distributed as
    1. I1 = RI / (R1 + R2)
    2. I2 = R1 I / (R1 + R2)
    3. where I is the net current that flows through the circuit.
  14. The total resistance of n equal resistances each of resistance r, in parallel, is:
    1. R = r / n
  15. For n equal resistances
    1. R series / R parallel = n2 / I
  16. The temperature coefficient of thermistors is negative and it is high.
  17. Resistivity increases with temperature.