THEORY OF EMF AND INTERNAL RESISTANCE

INTERNAL RESISTANCE of a cell is the resistance offered by the electrolyte of the cell when electric current flows through it.

ELECTROMOTIVE FORCE is the potential difference between the two poles of a cell in an open circuit (when no current is drawn from the cell). It is also defined as the energy supplied by the cell to drive a unit charge once around the circuit. It is denoted by E.

TERMINAL POTENTIAL DIFFERENCE IS the potential difference between the two poles of a cell in a closed circuit (when current is drawn from the cell).

When current flows in the circuit, there is a fall of potential across its internal resistance. Hence the PD is less than e.m.f. by an amount equal to potential drop across its internal resistance.

Definition: EMF of a cell is said to be one volt, if one joule of work is done by the cell to drive one coulomb of charge once around the circuit.

FOR MORE DETAILS, WHICH NEEDS EQUATION, PLEASE VIEW THE FOLLOWING DOCUMENT

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