Charge carriers
Charge & Current - OCR A-Level Physics
Key Definition
Charge carriers
The moving charged particles that carry current through a material.
The moving charged particles that carry current through a material.
- In metalsConductors in which the charge carriers are delocalised (free) electrons that drift when a p.d. is applied.: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). carriers are free (delocalised) electrons.
- In electrolytesSolutions or molten salts that conduct electricity via the movement of positive and negative ions.: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). carriers are positive and negative ions.
- In semiconductorsMaterials with resistivityA material property that quantifies how strongly it resists currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohm-metres (Ω m). between conductors and insulators. Their number densityMass per unit volume of a material. Measured in kg m⁻³.The number of charge carriers per unit volume in a material. Measured in m⁻³. of charge carriers increases with temperature.: charge carriers are electrons and holes.
- In insulatorsMaterials with very few free charge carriers, so they do not conduct electricity under normal conditions.: almost no free charge carriers exist.
Common Mistake
MEDIUM
Wrong: Saying 'electricity flows through the wire.'
Right: Say 'charge carriers (free electronsElectrons not bound to any particular atom, free to move through a conductor. Also called delocalised or conduction electrons.) flow through the wire' or 'currentThe rate of flow of charge. Measured in amperes (A). flows through the wire.' Be specific about what is moving.
Right: Say 'charge carriers (free electronsElectrons not bound to any particular atom, free to move through a conductor. Also called delocalised or conduction electrons.) flow through the wire' or 'currentThe rate of flow of charge. Measured in amperes (A). flows through the wire.' Be specific about what is moving.
Table comparing charge carriers in metals (free electronsElectrons not bound to any particular atom, free to move through a conductor. Also called delocalised or conduction electrons.), electrolytes (ions), and semiconductorsMaterials with resistivityA material property that quantifies how strongly it resists currentThe rate of flow of charge. Measured in amperes (A).. Measured in ohm-metres (Ω m). between conductors and insulators. Their number densityMass per unit volume of a material. Measured in kg m⁻³. of charge carriers increases with temperature. (electrons and holes), with an arrow showing increasing number densityMass per unit volume of a material. Measured in kg m⁻³.The number of charge carriers per unit volume in a material. Measured in m⁻³. from insulator to conductor.