Potentiometer

In the beginning, I thought about it in this way: Now that we got no current flowing, let's connect a resistor, then definitely nothing will happen and the slider will stay where is it. Fine, but I think my weakness is related to how exactly the voltage becomes zero, and some basic electricity concepts, because it was harder for me to think about it when G is off-balance.

Well, I'll try to write about how I "see" the situation which leads to V= 0 volt across. The slider with the unknown pd cell will show its max voltage at every point (lets say we can measure its voltage), but for the actual power supply, as we are varying L, so does its voltage across that points.

When both of the pd from cell and power supply are equal, electrons doesn't flow anymore, as pd = 0 V

Please go through my basic concepts and correct/add if you can. I believe understanding the real concept is the most important before solving any problem.

Thanks a ton!