NEET Class neet Answered
Figure shows a cell that has EMF E and internal resistance r is connected to rheostat through switch and Ammeter.
When switch is open there is no current flow in the circuit and the meaured voltage across terminals a nd B of cell equals to EMF E .
After closing the switch , voltage across the terminals a and b is measured by varying the current using Rheostat .
Terminal voltage is
As current increases , terminal voltage decreases because there is voltage across internal resistance .
It can be seen that voltage decreases linearly with increasing current .
The slope of the graph is internal resistance of cell . Y-intercept is voltage when current is zero .
Hence Y-intercept is internal resistance of cell .