A variable resistor is a resistor whose resistance can be adjusted by turning a knob. In a certain experiment a battery is connected to a variable resistor R. The potential difference across the resistor and the current through it are recorded for a number of settings of the resistor knob. Assume the battery can be modeled as an ideal potential source in series with an internal resistor.
Consider the following possibilities:
I. a small external resistance
II. a large external resistance
III. a small total current
IV. a large total current
When would it be a good approximation to ignore the internal resistance of the battery?