Using the simulation in class / Teaching the relationship between charge and current

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HEADLINE LEARNING POINTS

  • A current is just moving charges

  • The faster the charges move, the bigger the current (or vice-versa)

UNDERSTANDING

  • The charges are already there everywhere in the circuit, because they are part of the atoms that make up the wires

  • They all start moving everywhere at the same time

  • They move very slowly

USING THE SIMULATION

  • Uncheck the ‘Show energy’ checkbox

  • Start with the voltage at zero and gradually increase it

  • Ask students:

    • Where do the charges start moving first?

    • How fast do they move?

    • Do they move at the same speed everywhere in the circuit?

    • What would happen if the charges moved at different speeds in different parts of the circuit?

SUBTLETIES

  • Each black dot represents one coulomb of positive electric charge

  • The simulation shows conventional current

  • Current is not just about the speed of the charges, but the number of coulombs of charge that pass a point on the circuit each second

  • In a real circuit, the conducting parts are different diameters and are made from different materials, so the speed of the charges is different in different parts of the circuit

  • A bigger current will still mean faster charges in each part of the circuit

MISCONCEPTIONS

  • The biggest misconception is that the wires start empty, and that the charges come from the battery

  • It’s common to justify the fact that circuits start working straightaway by assuming that the charges move very quickly from the battery

  • The simulation clears up other misconceptions without needing to draw attention to them, for example that the current gets used up or that it flows from each side of the battery.