Our class conducted and experiment to investigate internal resistance and terminal pd, using a cell, fixed resistor and variable resistor. The results were as follows:
As the resistance of the variable resistor was increased, the current through the circuit decreased. (As using E=I(R+r), for emf E to remain constant, if R increases, current I must decrease). Note: E=emf, I=current, R=external resistance(I.e the fixed and variable resistor) and r=internal resistance.
As current decreasesd, voltage across the internal resistance of the cell, Ir, decreased (using V=IR), because internal resistance should remain constant. Therefore voltage across the terminals increased (as less is wasted across the internal resistor).
When plotting a graph of terminal pd(y) against current(x), a linear relationship was shown: as current increased terminal pd decreased.
The gradient gives the (-)internal resistance, which was constant.
However here's the problem, when calculating internal resistance using the values ( with r=(E-V)/I ), the internal resistance increased as current decreased (as external resistance increased). It did not remain constant. The individual internal resistances did not match the internal resistance calculated through the gradient, and I do not know why.