The Physics
Opus in profectus

Batteries in Circuits

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series: add voltges. A battery is a series of cells.

parallel: add currents — sort of. This is not a good way to store batteries, by the way.

internal resistance

V = ℰ − Ir


V =  terminal voltage, the voltage that you actually get out of the battery under operating conditions, the voltage that you'd measure across the terminals
ℰ =  electromotive force (emf), the ideal voltage of the battery, the electic potential difference caused by the chemical reaction taking place inthe battery, a number that chemists learn to compute
I =  current, the load that the battery is delivering to the circuit
r =  internal resistance, every part in a circuit has some resistance — even batteries, which are normally thought of as pure voltage elements