Electrical Circuit
Electricity and Magnetism

The electrical flow - all together now!

Teaching Guidance for 14-16 Supporting Physics Teaching

The flow starts simultaneously everywhere in the loop

Wrong Track: When the switch is closed, the electric current flows out of the battery, then goes through the wires, then comes to the bulb and then flows back to the battery.

Right Lines: When the switch is closed, the charged particles are set in motion in all parts of the circuit, all at very nearly the same time.


Thinking about the learning

An absolutely fundamental point in coming to understand electric circuits is that when a circuit is completed the electric charge starts flowing in all parts of the circuit: there is a current in every element. All charged particles start their gradual drifting movement at very nearly the same time.

The wrong track thinking illustrated here is based on the idea that the battery acts as the source of action for the circuit. This basic idea is, in fact, correct: the bulb will not light without a battery. The clear point to make here is that the battery is not the source of charge. The charge that makes up the electric current do not start off in the battery – it is present in all parts of the circuit (bulbs, and wires and cells).

Thinking about the teaching

It's all too easy for the teacher to unconsciously promote the battery–as–source–of–charge model by consistently pointing, with one finger, to the battery and saying,

Teacher: So the electric current flows from the battery… round the circuit…


Teacher: So the electric charge flows from the battery… round the circuit…

Such descriptions are to be avoided.

A more helpful approach is to portray the all–at–once motion of the current with two hands to demonstrate the simultaneous motion of charge in all parts of the circuit.

The rope loop model introduced in the SPT: Electric circuits topic provides a very striking representation of this all–at–once motion.

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