Egg Carton Analogy — Conventional vs Electron Current
Eggs hop one cup at a time along a carton that has a single empty cup in it. Watch the eggs and everything moves one way; watch the empty cup and it walks steadily the other. Nothing at all is moving that way, yet "the gap moved" describes what happened perfectly — which is exactly the situation a current is in.
How to use this simulation
- Choose Watch the eggs to follow the real carriers hopping one way
- Choose Watch the empty space to follow the gap travelling the other way
- Choose Both at once to see the two descriptions running over the same motion
- Step slowly through a few hops to check that no cup is ever occupied twice
What to look for
- Each egg only ever moves one cup, yet the gap crosses the whole carton
- The gap always travels in exactly the opposite direction to the eggs
- Counting hops gives the same rate of transfer whichever description you use
- Nothing physical moves in the gap's direction — it is a bookkeeping device that happens to work
- Electron flow and conventional current stand in precisely this relationship in a wire
The physics behind it
Charge transport can be booked in two equivalent ways. Electrons carry negative charge and drift from the negative terminal towards the positive one; the same transfer is described by imagining positive charge moving the opposite way, and that is the conventional current. Neither account is more true than the other — the carrier's sign and its direction enter the current only as a product, so flipping both leaves I unchanged. Circuit theory settled on the conventional choice long before the electron was discovered, and every formula and meter still assumes it.