Simulation · Physics · Class 12

Two cells: in series, in parallel, and one reversed

From the lesson Cells in series and in parallel in Current Electricity. Change the values and watch what happens.

The idea behind it

NCERT § "Cells in Series and in Parallel"

Two cells in series (positive of one to negative of the next) behave like one cell of emf ε_eq = ε₁ + ε₂ and internal resistance r_eq = r₁ + r₂.
If one cell in a series pair is reversed, its emf is subtracted: ε_eq = ε₁ − ε₂, while the internal resistances still add.
For n identical cells in series: emf nε and internal resistance nr.
Two cells in parallel (like terminals together) behave like one cell with ε_eq = (ε₁r₂ + ε₂r₁)/(r₁ + r₂) and r_eq = r₁r₂/(r₁ + r₂).
The parallel formula can be written 1/r_eq = 1/r₁ + 1/r₂ and ε_eq/r_eq = ε₁/r₁ + ε₂/r₂; if one cell is reversed, its ε changes sign.
For n identical cells in parallel: emf ε and internal resistance r/n.
When two cells of unequal emf are joined in parallel with no external load, a current circulates between them, driven through the lower-emf cell by the higher-emf one.

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