Emf, internal resistance and

Terminal potential difference of a cell

 


1) Suppose there is cell and it is connected to a resistors of resistance R as shown in below:





2) When the circuit is on, current will start flowing through it. Say that amount of current is I.



3) Now cell is free and there is no connection to it. When cell is free the potential difference between the two electrodes is called the emf or electromotive force of the cell.



4) When current flows it passes through the resistors (R) and also through the cell.



5) Due to the electrolytes presents in the cells, cell electrolytes offers a resistance (r).




6) Due to this cell resistance the actual potential difference drops, this New potential difference is

V = e -Ir

Where e is the emf of the cell


Ir potential due to internal resistance of the cell

 


7) Now V potential is equal to the potential across the resistance R so

V =  IR

 


Now finally got

V = e -Ir

IR = e -Ir

IR + Ir = e