Electric Current & Electron Flow (OCR A Level Physics)

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

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

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

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