Calculating the current in whole circuit loops

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.