How to play Battery Stack
- Choose a test and read the cells and how they sit on the card.
- Add voltages in a row, subtract a flipped cell, take one cell's voltage side by side, and use W = Q·V for energy.
- Type your prediction and press Start. The cells slide in, the voltmeter reads, and the switch closes.
- Compare the voltmeter, the lamp, and the staircase with your orange prediction.
Voltage and cells
A cell lifts every coulomb of charge that goes through it to a higher potential, by its voltage: a 1.5 V cell gives each coulomb 1.5 J. Put cells in a row, each + end touching the next − end, and the lifts add up like the steps of a staircase, which is why a torch with four 1.5 V cells runs on 6 V. Turn one cell round and it becomes a step down, cancelling one of the others. Put identical cells side by side and they all join the same two points, so the voltage stays that of one cell, though they can keep the current going for longer. A battery's voltage tells the energy it gives the charge it moves: W = Q·V, so a 9 V battery gives 9 J to each coulomb. Cells only come whole, so to reach a voltage you round up to the next cell.
A focused learning model
The cells are ideal, with no internal resistance, so the voltage never changes with the current; the wires are ideal, the voltmeter takes no current, and the lamp is a fixed resistance. The cells click into the holder one after another over 2 s and count once fully in; the switch closes at 2.5 s, and the current is steady at once. In the energy test the switch is closed from 1 s to 3 s with 0.25 A flowing. The lamp glows in step with its power. The electron dots move at a speed in step with the current, not at the real drift speed, which is far slower. Answers within 2% are right; the number of cells must be exact.