Electromagnetism- Resistance Laws

Resistance Laws

In seriesR_s= R₁+ R₂+ ... + R_n

In parallel1/R_p= 1/R₁+ 1/R₂+ ... + 1/R_n

R_p= R₁R₂/(R₁+ R₂)

If there are n equal resistances in seriesR_s= nR

If there are n equal resistances in parallelR_p= R/n

Terminal potentialV = ε - Iris the potential drop across a resistance.

ris internal resistance andεis 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,

ThenI = nε / R + nrwhere R is external resistance

Cells in parallel: -if n cells (identical) are in parallel each having emfεand 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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