could you plz explain the concept of terminal voltage with respect to internal resistance and external resistances.

Asked by Pushkal Shukla | 27th Apr, 2014, 05:11: PM

Expert Answer:

When current is drawn from a cell, i.e., when the cell is in closed circuit, the potential difference between the electrodes of the cell is called its terminal voltage.(V)
When current is drawn from a cell, it flows from anode to cathode in the external circuit and from cathode to anode inside the cell through the electrolyte so as to maintain a continuous flow.
The resistance offered by the electrolyte inside the cell, to the flow of current is called the internal resistance of cell. It is denoted by r
The electromotive force (emf) is the potential difference of a source when no currentis flowing.Let E be the emf of the cell.
If I is the current drawn from the cell of internal resistance r, the voltage drop is v=Ir
Total resistance of the circuit is the sum of both internal and external resistance ,= R+r
When current flows through the circuit , there is a fall of potential across the internal resistance of the the cell .The potential difference between the two poles of the cell is less than the emf of the cell by an amount equal to the potential drop across the internal resistance. Therfore the terminal potential difference of a cell is always less than its emf.
 ie Terminal voltage V = emf - Ir. 
                             V= E -Ir
Since V=emf−Ir, terminal voltage equals emf only if there is no current flowing.

Answered by  | 28th Apr, 2014, 09:37: AM

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