COMBINATIONS OF RESISTORS (CURRENT ELECTRICITY)

INTERNAL RESISTANCE OF A CELL: 

The internal resistance of a cell is the resistance of the electrolyte between the anode and cathode. The magnitude of internal resistance of a cell  depends on : 
1) The distance between the plates (r\(\alpha\) d) 
2) The area and size of the plates \(\left( {r\alpha \frac{1}{A}} \right)\)
3) Nature of electrolyte, 
4) Strength of the electrolyte or concentration  \((r \alpha c)\)
5) Area of the crosssection of the electrolyte through which current flows. 
6) Internal resistance depends on temperature. It decreases with increase of temperature. The internal resistance of a cell can be accurately measured using a potentiometer.

Note-
An ideal cell is that which has no internal resistance. i.e., internal resistance r= 0 for an ideal cell. 

Note-
The difference between a new torch light cell and an old one is not in the emf. The decrease in emf will be very small. But, the difference is due to increase in internal resistance. After a prolonged use, the internal resistance increases by a factor 10³.