Electrical properties Flashcards
Typical resistivity of conductors
Have resistivities less than 10-4 Ωm
Typical resistivity of Semi-conductors
Resistivities in the range 1010 to 10-4 Ωm
Typical resistivity of Insulators
Resistivities larger than 1010 Ωm
What is the equation for Electric field strength?
E = V/l
What is the equation for Resistivity?
R = ρl/ A
What is Metal conduction?
Movement charge through electrons
What is meant by Ionic solutions conduction?
Movement of charge through positive and negative ions
What is meant by Semi-conduction?
Movement of charge through electrons and holes
What is the equation for Conductivity?
σ = nqµ
Effect of temperature in metals
Reduces conductivity as atoms vibrate causing greater electron scattering.
The change in resistivity of the metal with temperature is approximately linear.
Impurity atoms in the metal disrupt the crystal structure and result in increased scattering of the electrons
Effect of metal processes
Deformation of the metal also increases its resistivity by the introduction of dislocations
This effect is less significant than for impurities
Hence to strengthen a metal that requires high electrical conductivity, it is better to strengthen it by work hardening
What is meant by Critical temperature?
Temperature at which some materials have zero resistivity and hence become superconducting
Issues with high temperature super conductors
Have complex crystal structures, often involving missing atoms.
Mechanism not fully understood – hence difficult to make improvements.
There is a critical current density, above which they are no longer superconducting, even if below Tc.
What is Doping?
Adding small quantity of impurity to a pure semi-conductor. Becomes ‘extrinsic’
The presence of additional holes and electrons leads to increased conductivity
How can materials have many charged particles but be insulators?
The ions are locked into place
