Parallel cells: internal resistance

EMF & Internal Resistance — AQA A-Level Physics

Cells in parallel provide a longer-lasting energyThe capacity to do work. Measured in joules (J). supply.
The total store of chemical energyThe capacity to do work. Measured in joules (J). is greater.
For n identical cells in parallel, EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). stays the same as one cell.
Each cell only carries a fraction of the total currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A)..

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CurrentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). through each $cell = I/n (splits equally$ for identical cells).
Lost voltsThe potential differenceThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). across the internal resistanceThe opposition to currentThe rate of flow of charge. Measured in amperes (A). flow. The ratio of potential difference to current. Measured in ohms (Ω).The resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). within the source of EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). itself, which causes energy to be dissipated inside the source. of a cell. Equal to Ir. in each $cell = Ir/n (reduced because current$ is shared).
Net effect: same EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V)., lower internal resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω).The resistance within the source of EMF itself, which causes energy to be dissipated inside the source., longer battery life.
This is why car batteries use cells in parallel — high current, low internal resistanceThe resistance within the source of EMF itself, which causes energy to be dissipated inside the source..

Common Mistake MEDIUM

Students often: Thinking parallel cells double the EMF.
Instead: Parallel identical cells keep the same EMF. Only the internal resistance is reduced (r/n). Series cells add EMFs.