initially- with positive potential differences - the current is directly proportional to the p.d. However, as the current through the filament increases, the heating effect caused in the lamp also increases and so the temperature of the filament rises. This increase in the filament's temperature also increases the resistance of the filament. As a result the rate of increase of the current decreases and a greater change in the potential difference is required to cause a change in the current. This can be seen on the curve as the gradient becomes more shallow (greater resistance). This same pattern is repeated when a negative potential difference is applied across the filament
Coulombs law says that the force between any two charges depends on the amount of charges and distance between them. This force is directly proportional to the magnitude of the two charges and inversely proportional to the distance between them.
where are charges, is the distance between them and k is the coulomb constant.
case 1:
case 2
case 3:
Comparing the 3 cases:
The maximum potential force according to coulombs law is between -1 charge and +3 charge separated by a distance of 100 pm.