Moving charges

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  • Moving Charges
    • Electric current in metals
      • Models  describe the movement of charge carriers through materials
      • In metals, electric current is the flow of electrons
        • Most remain fixed to their atom
        • Some are free to move (delocalised)
      • Positive ions are fixed but are able to vibrate around points causing temperature rise
      • The greater the rate of charge flow, the greater the electric current in the wire
      • A larger current may be due to
        • A greater number of electrons moving past a given point per second
        • The same number of electrons moving faster
    • Conventional current and electron flow
      • Conventional current is the movement of current from a positive to a negative terminal
      • Direction of all electric currents is still treated as positive to negative, regardless of movement of charge carriers
      • In metals, electrons travel from the negative to the positive terminal, the opposite of conventional current
    • Electric current in electrolytes
      • Liquids that carry electric currents are called electrolytes. The charge carriers are ions
      • Electrolytes are either molten ionic compounds or ionic solutions e.g. salt in water
      • If a positive electrode (anode) and negative electrode (cathode) are placed in the solution, ions are attracted to them
        • Positive ions (cations) move to the cathode
        • Negative ions (anions) move to the anode
      • There is a flow of charge, therefore, a circuit
      • Cations accept electrons from the cathode and anions donate electrons to the anode. This means electrons can carry electric charge in the metal part of the circuit
    • Measuring electric current
      • Current at any point in a circuit is measured using an ammeter
      • It is placed in series at the point the current is being measured
      • They should have the lowest possible resistance
        • Reduces the effect on the current it measures
        • An ammeter with a high resistance reduces the current it is measuring
        • 0 resistance means it has no effect on the current it measures

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