Electrical Circuit
Electricity and Magnetism

What gets used up?

Teaching Guidance for 11-14 Supporting Physics Teaching

Current is used

Wrong Track: The electric current gets used up in the bulb to make it work.

Right Lines: Current is the same in each element and energy is shifted. The current in the wire after a bulb has the same value as the current in the wire before the bulb because the same number of charged particles enter and leave the bulb each second. What goes in must come out! Charge is conserved. However, as each charge passes through the bulb, energy is shifted by the filament as it glows.

Current the same everywhere

Thinking about the learning

The incorrect idea here is that the current after the bulb is less than the current before the bulb, because some of the current gets used up to make the bulb work.

It is clear to most pupils that something must get used up when a battery is connected to a bulb and the bulb lights up. The key learning challenge is for pupils to come to understand that the electric charge is conserved whilst energy is shifted by the circuit.

Thinking about the teaching

To communicate the idea that electric current is the same everywhere in the circuit, it is helpful to make practical measurements of electric current and to relate these to the electric circuit model and to the teaching model. So there are three facets to think about.

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