Height is potential difference. Width is current. Turn the circuit and both are visible at once.
The cell is an escalator that lifts charge 6 V; every component is a step back down. Charge goes round a closed loop, so whatever height it loses across the components it regains at the cell. On a flat page you can draw height or width — which is why the series and parallel rules usually arrive as two separate things to memorise. Here you can turn the circuit and see both, and the two rules become one picture.
Drag any circuit to orbit; all three turn together so they stay comparable. Front is the familiar staircase, Plan looks straight down so the lane widths are the whole story, and Charge flow switches between the two halves of I = nAvq.
| Component | R / Ω | I / A | p.d. / V |
|---|---|---|---|
| R1 | 2.0 | 1.0 | 2.0 |
| R2 | 3.5 | 1.0 | 3.5 |
| R3 | 0.5 | 1.0 | 0.5 |
| Whole loop | 6.0 | 1.0 | 6.0 |
| Branch | R / Ω | I / A | p.d. / V |
|---|---|---|---|
| A | 6.0 | 1.0 | 6.0 |
| B | 3.0 | 2.0 | 6.0 |
| C | 2.0 | 3.0 | 6.0 |
| Whole circuit | 1.0 | 6.0 | 6.0 |
| Series | Parallel | |
|---|---|---|
| Heightpotential difference | Different — each component takes its own share of the 6 V. Look at the staircase: 2.0 V, then 3.5 V, then 0.5 V, and the charge is back on the floor. | The same — every branch starts at the top rail and ends on the floor, so each one falls the whole 6 V. Three drops of identical height. |
| Widthcurrent | The same — one lane all the way round, so the same 1 A passes every point. Charge is not used up in a resistor; it is only let down. | Different — the narrowest branch is the largest resistance. Widths 1 A, 2 A and 3 A leave the rail, and 6 A returns to the cell. |
Because the series current is exactly 1 A, each step's height in volts is numerically its resistance in ohms — a 3.5 Ω resistor drops 3.5 V. Students can check V = IR by eye before they write a line of working. Watch the top rail in the parallel view too: it starts 6 A wide and narrows to 5 A, then 3 A, as each branch takes its share.
Real circuits are rarely one or the other. Every charge here must pass R1 — that is the series part, and it takes 3.0 V from the full 3 A. Then the loop splits and the two branches share what is left: the same 3.0 V each, with the 1.5 Ω branch carrying twice the current of the 3 Ω one. Turn it to the front and you see one tall step followed by two short ones of equal height; turn it overhead and you see one wide lane becoming two of different widths.
| Component | R / Ω | I / A | p.d. / V |
|---|---|---|---|
| R1 in series | 1.0 | 3.0 | 3.0 |
| R2 branch | 3.0 | 1.0 | 3.0 |
| R3 branch | 1.5 | 2.0 | 3.0 |
| R2 in parallel with R3 | 1.0 | 3.0 | 3.0 |
| Whole circuit | 2.0 | 3.0 | 6.0 |
Built for P2 Electricity, 2026. Resistor blocks are coloured by the first band of the resistor colour code — brown 1, red 2, orange 3, green 5, blue 6. No third-party material.