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Electric Current

AQA AS-level PhysicsTopic 13 of 1420 lessons

Revision notes for Electric Current in AQA Physics (7407). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. Electrical ConductionElectrons are the charge carriers in metals.
  2. Electric Current and Electric ChargeCurrent is the flow of charge.
  3. Charge CarriersInsulators No electrons move through insulators because there are no free electrons that can move through the solid lattice.
  4. The Emf of a SourceThe emf (electromotive force) ε of a source is the energy transferred into electrical energy per unit charge passing through the source, ε = W/Q.
  5. Potential DifferenceThe potential difference is the energy transferred per unit charge by the charge carriers to the component.
  6. Energy TransferThe electrical power is the energy transferred per unit time by the charge carriers to the component.
  7. Electric PowerThe electrical power is the energy transferred per unit time by the charge carriers to the component.
  8. ResistanceThe electrical resistance of a component is a measure of its opposition to the flow of electric current through it.
  9. Measuring Resistanceresistance = p.d. across component current through component R = V I ohms = volts amps The current is varied using a variable resistor and measured…
  10. Ohm's LawOhm's law states that the current through a metallic conductor is directly proportional to the potential difference across it, provided that its…
  11. ResistivityR = ρ L A resistance = resistivity × ;length(m) cross-section area(m2). ρ is resistivity, L is the length of the wire and A is the cross-sectional…
  12. SuperconductivitySuperconductor materials have zero resistivity below a critical temperature e.g. about 134K (-139°C) for compounds containing mercury, barium…
  13. Electronic ComponentsMany electronic components are used to control the current and potential difference in a circuit.
  14. Investigating the Characteristics of ComponentsTo measure the variation of current with potential difference for a component, either a potential divider circuit or a variable resistor can be used…
  15. IV GraphsA current-potential difference graph, or IV graph, shows how the current through a component changes as the p.d. across it is varied.
  16. Fixed ResistorsWhen an IV graph is plotted, a wire gives a straight line through the origin.
  17. Filament LampThe I-V graph for a filament lamp is a non-linear, s-shaped curve passing through the origin, because the current is not directly proportional to…
  18. Thermistors and Light Dependent ResistorsA thermistor is made from a semiconducting material, usually a mixture of metal oxides.
  19. DiodesThe current through a diode is measured for a range of potential differences in both the forward and reverse bias.
  20. Resistance and TemperatureThe resistance of a metal increases with temperature.

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