Electric Current & Electron Flow (OCR A Level Physics)

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Defining Current

  • Electric current is the rate of flow of charge carriers
  • This is defined as the movement of
    • Electrons in metals
    • Ions in electrolytes

Electrons in Metals

  • In metals, such as copper, mercury and titanium, the flow of charge is made up of electrons
  • The metal ions are closely packed and arranged in a crystal lattice structure
  • The atoms have many free (delocalised) electrons that are free to move randomly
    • These are sometimes known as conduction electrons
    • These are what makes metals good conductors of electricity

  • When conducting electricity, meaning one side of the metal is attaching to a negative terminal and the other to a positive, the conduction electrons drift slowly through the metal creating a current

Metal Free Electron Conduction, downloadable AS & A Level Physics revision notes

Free electrons in metal create current flow

Ions in Electrolytes

  • Ions are atoms that have lost or gained an electron. This means they are either:
    • An anion - a negative ion (gained an electron)
    • A cation - a positive ion (lost an electron)

  • An electrolyte is a substance that produces an electrically conducting solution
    • The charge carriers are not electrons, but cations and anions

  • An example of an electrolyte is copper sulfate dissolved in water

Electrolyte Conduction, downloadable AS & A Level Physics revision notes

Anions are attracted to the anode and cations to the cathode

Current & Electron Flow

  • In electrical wires, the current is a flow of electrons
  • Electrons are negatively charged; they flow away from the negative terminal of a cell towards the positive terminal
  • Conventional current is defined as the flow of positive charge from the positive terminal of a cell to the negative terminal
    • This is the opposite to the direction of electron flow, as conventional current was described before electric current was really understood

 

Electric current flow, downloadable AS & A Level Physics revision notes

By definition, conventional current always goes from positive to negative (even through electrons go the other way)

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.