Pathways and compensation
Physics Narrative for 14-16
Compensation – one factor diminishing to compensate for growth in another
The power in a pathway depends on both the current and the potential difference. This allows a choice: there can be the same power in different characters of pathway. You can choose cells and lamps or resistors to get a large current but a small potential difference; or a small current but a large potential difference. This is a good example of compensation in action. Compensate for changes in one quantity by making inverse changes in the other. For example, making the current larger allows you to reduce the potential difference, but still have the same power in the pathway.
Back to why circuits are so pervasive
Later we'll see how choosing the character of the pathway allows particular tasks to be performed more effectively. Electric circuits are so common because we can control how and where the power is switched, so any chance to control that power better should be taken. Altering the character of the pathway, by selecting a large or small potential difference, with a resulting small or large current, is one such clear chance.
To shift energy over long distances, say for the National Grid, choosing the character of the pathway determines how much power stays in the electrical pathway and how much is switched to other pathways. We don't want any power in the heating by particles or heating by radiation pathways en route – only when the loop passes the consumer. At this point in the loop, consumer appliances switch to these pathways.