Section 1: Conduction Flashcards
Electric current
The rate of flow of charge
Q=IT
Current time graph, area =charge
A coulomb is the total charge supplied by 1A in 1S
Conductors
Massive number of free electrons
E.g. Copper
Semiconductors
Properties of metals and non-metals, resistance decreases with temp.
E.g. Silicon or Germanium
Insulators
No free electrons
E.g. Plastic, Rubber or Polystyrene
Thermal velocity
No current so velocity depends on temp.
Drift velocity
Current is applied, free electrons collide more with ions.
Mechanism of conduction
1) in metals each atom has a loose electron
2) no current = free electrons move due to temp – THERMAL VELOCITY
3) voltage applied, electric field produced, free electrons move towards + end
4) free electrons collide with ions, slowing them down and causing them to drift – DRIFT VELOCITY
The effect of temperature on conduction
1) higher temp, higher amplitude of vibration in lattice ions, therefore larger collision cross-section for electrons and electrons collide more frequently
2) higher temp, higher THERMAL VELOCITY of free electrons, therefore more collisions
The cause of resistance
When free electrons collide with ions, they slow down and increase DRIFT VELOCITY
I=nAve
1) volume=lA
2) free electrons=nlA
3) charge=nlAe
4) time =l/v
5) Q=IT – I=Q/T
6) SUB I=nlAe/l/v – nAve
Number of electrons per coulomb
1 divided by 1.6x10^-19
