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Question
Illustrate-combination of cells e.g., three cells, in series, explaining the combination briefly. Obtain an expression for current ‘i’ in the combination.
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Solution
Combination of cells in series:
In this combination, the cells are so connected that the negative terminal of one cell is connected to the positive terminal of the other cell such that in the end one free positive and one free negative terminal are left. These free terminals are connected to the external circuit. If the e.m.f of each cell is E and Y be the internal resistance and I be the current, then e.m.f. of the cell in series = nE (here n = 3)
The total internal resistance = nr
and External resistance = R
∴ Current I in the external circuit `= "Total e.m.f."/"Total resistance of the circuit"`
I = `"nE"/"nr + R"`
If r is very small, then neglecting r, we get I = `"nE"/"R"`
This shows that it is advantageous to connect cells in series to get a large current when their internal resistance is negligible.
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