Calculating the current in whole circuit loops(Exposition)



Words follow actions

To make things memorable and to emphasise the physics, just follow what you do.

Talk through your action in building a circuit. The relationship between potential difference, resistance and current for the circuit may then make more sense.

Choose a cell, then choose a lamp. Build them into a loop circuit and find that the current in the lamp, and in the wires, and in the cell, is set by these choices.

So VR tells I what to be.

Written more conventionally:

I = VR

Now perform two quick checks:

As V gets closer to zero, so I gets closer to zero.

As R gets closer to zero, so I becomes very large.

These simple checks show that the relationship correctly represents what you observe in the circuits.

What you can choose:

  • A potential difference: select the cell.
  • A resistance: choose a resistor or lamp.
  • What you cannot choose:

  • A current–that is the result of your first two choices.


  • Prepare for teaching across the topic using these links

    topic kitset topic path core ideas (topic) decisions to make (topic) suggestions (for the topic) topic issues



    This is a nugget in the PN thread – connect all three threads from any link

    Physics Narrative (PN) Teaching & Learning Issues(TL) Teaching Approaches(TA)

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