Factors on which the internal resistance/emf of a cell depends
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Internal Resistance of cell & Combinations of Cells
Internal Resistance of a cell:
The opposition offered by the electrolyte of the cell to the flow of electric
current through it is called the internal resistance of the cell.
Factors affecting Internal Resistance of a cell:
i) Larger the separation between the electrodes of the cell, more the length
of the electrolyte through which current has to flow and consequently a
higher value of internal resistance.
ii) Greater the conductivity of the electrolyte, lesser is the internal resistance
of the cell. i.e. internal resistance depends on the nature of the electrolyte.
iii) The internal resistance of a cell is inversely proportional to the common
area of the electrodes dipping in the electrolyte.
iv) The internal resistance of a cell depends on the nature of the electrodes.
R
E r
I I
E = V + v
= IR + Ir
= I (R + r)
Cells in Parallel combination:
Cells are said to be connected in parallel when they are joined positive to
positive and negative to negative such that current is divided between the cells.
NOTE:
1. The emf of the battery is the same as that of a
single cell.
2. The current in the external circuit is divided equally
among the cells.
3. The reciprocal of the total internal resistance is the
sum of the reciprocals of the individual internal
resistances.
Mixed Grouping
Let n be the no. of cells in series in each row and m be
the no. of such rows. Let E be the e.m.f. of each cell
and ‘r’ be the internal resistance of each cell.
In each row, there are n cells in series, therefore their
total resistance is ‘nr’ and total e.m.f. in nE.
Thus are ‘m’ rows of cells in parallel, therefore total
internal resistance of all the cells