Electrical Circuit
Electricity and Magnetism

Power brings together the current and voltage stories

Teaching Guidance for 11-14 Supporting Physics Teaching

Power is determined by current and voltage

Thinking about the learning

The idea of electrical power brings together the moving charge (current) part of the electric circuit story along with the energy shifted (voltage) part. As such, pupils often find this a satisfying step to make as they draw on their knowledge of current and voltage and see how this leads to an understanding of electrical power.

Thinking about the teaching

For those pupils who are able to follow the line of argument, we would recommend, following through the working from first principles approach, which is set out in the Physics narrative(from current and voltage to power.

Start with the definitions of current as coulomb per second and voltage as joule per coulomb and move from these to power in terms of joule per second. Such an approach is made easier in the classroom by referring to a particular circuit (as we did in the narrative) and working with specific figures for current and voltage (for example: 2 ampere and 12 volt). Having developed the idea of power for a specific case, you can then introduce the general definition.

All too often, pupils know that power can be calculated by multiplying together current and voltage, but have little understanding either of why this should be the case or what the electrical power actually means in practice.

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