4.1.2 Mean Drift Velocity

• Electric conduction properties depend on the number density of a material:

  The number density is the number of free charge carriers per unit volume

  greater the number density = better conductor
• Classified into 3 groups:

  Conductors: Have a very high number density = *10^28 m ^-3

  Semiconductors: Have a value inbetween = *10^17 m^-3

  Insulators: Have a much lower value = *10^9 m^3
• Mean Drift Velocity: is the average displacement per unit time of an charge carrier passing through a object
• Mean Drift Velocity is proportional to current, if current increase rate of flow of charge carriers increases

  therefore average velocity of an electron increases
• Mean Drift Velocity is inversely proportional to number density, as the greater number of free electrons per m^3, the more collisions therefore V lowers
• Mean Drift Velocity is Inversely proportional to cross sectional area, as in a larger area are more particles therfore more collisions whereas in a smaller are less collisions so V increases
• I = A*n*e*v

  I = current A

  A = cross sectional area m^2

  n = number density m^-3

  e = elementary charge

  v = mean drift velocity ms^-1