INTERNAL RESISTANCE OF A CELL | Determination of internal resistance of a cell using voltmeter
This Physics Animation will helps you to understand how an Internal resistance of a cell works. The electric current in an external circuit flows from the positive terminal to the negative terminal of the cell, through different circuit elements. In order to maintain continuity, the current has to flow through the electrolyte of the cell, from its negative terminal to positive terminal. During this process of flow of current inside the cell, a resistance is offered to current flow by the electrolyte of the cell. This is termed as the internal resistance of the cell.
A freshly prepared cell has low internal resistance and this increases with ageing.
---------------------------------------------------------------------------------------
Determination of internal resistance of a cell using voltmeter
---------------------------------------------------------------------------------------
The circuit connections are made as shown in animation. With key K open, the emf of cell E is found by connecting a high resistance voltmeter across it.
Since the high resistance voltmeter draws only a very feeble current for deflection, the circuit may be considered as an open circuit. Hence the voltmeter reading gives the emf of the cell. A small value of resistance R is included in the external circuit and key K is closed. The potential difference across R is equal to the potential difference across cell (V).
