Resistance Laws
In series Rs = R1 + R2 + ... + Rn
In parallel 1/Rp = 1/R1 + 1/R2 + ... + 1/Rn
Rp = R1R2/(R1 + R2)
If there are n equal resistances in series Rs = nR
If there are n equal resistances in parallel Rp = R/n
Terminal potential V = ε - Ir is the potential drop across a resistance.
r is internal resistance and ε is emf of the cell.
Normally terminal potential is less than emf. But during charging of a cell terminal potential is greater than emf.
Cell in series: - if n identical cells each of emf ε are connected in series each having internal resistance r,
Then I = nε / R + nr where R is external resistance
Cells in parallel: - if n cells (identical) are in parallel each having emf ε and internal resistance r.
Cell in mixed grouping m rows of n cells each are connected to an external resistance R. assuming all cells are identical each having emf ε and internal resistance r as shown in
I = nε/[nr/(m + R)]
Maximum power is delivered by a cell/source if external resistance = internal resistance.
Maximum current is delivered when short circuited (external resistance = zero).
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