Calculating the current in whole circuit loops
Physics Narrative for 14-16
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.