Case I: a negative conductor makes contact with a neutral conductor. Negative donates some electrons to neutral, until there is 0 potential difference. Then they both are slightly negative. This happens quickly. (Assuming they are good conductors.)

enter image description here Case II: the neutral conductor is grounded (via a resistor) to earth. When they make contact, all surplus electrons drain to earth.

How does the resistor affect the movement of electrons? Will both conductors reach equipotential first, before surplus electrons drain to earth? (Because they make contact with each other without a resistor in between. The resistor is between them and earth.)


To understand what happens during a transition, you'll need to go back to the basics.

The negative conductor initially has a surplus of electrons. These electrons don't like to stay close to each other and given enough time they will adopt a configuration which minimizes the potential energy as much as possible. In this case, that configuration is where the charge spreads out on the surface of the conductor. It would be even better if the electrons left the conductor but unfortunately, the poor electrons are bound to the conductor.

When you bring the negative conductor in contact with the neutral conductor, the charges on the surface near the point contact immediately get pushed into the neutral conductor. As of now, the electrons aren't aren't aware of the fact that the neutral conductor is grounded. The electrons keep moving into the neutral conductor. As the electrons near the point of contact move into the neutral conductor, the electrons near the near the point of contact see that the electron density is decreasing, hence, they start moving closer to the point of contact and then ultimately to the neutral conductor. At one point when the electron density reaches a certain point, the electrons in the conductor which was once neutral face repulsive forces and this push them into the wire and they start flowing into the ground.

As time passes, all the charge would have left both the conductors as the earth can be considered to be a big sink. This would leave both the conductors neutral and with zero potential.

  • $\begingroup$ Thanks! Yes, as time passes all surplus electrons go into earth. Before electrons flow into that big sink, does the resistor limit the speed at which the electrons move from the negative conductor to the neutral conductor? Or is the interaction between the conductors only a result of electron density? $\endgroup$ – Marty Mar 5 '17 at 14:58
  • $\begingroup$ In other words: when 2 good conductors make contact, they almost instantly become equally charged. But does this also happen when the neutral conductor is grounded to earth? So, first they get equally charged and then the surplus electrons flow into earth? $\endgroup$ – Marty Mar 5 '17 at 14:59
  • $\begingroup$ They probably won't become equal. I need to do some rigorous thinking and derivations to check that. $\endgroup$ – Yashas Mar 5 '17 at 15:16
  • $\begingroup$ Thanks. Haha, that won't be needed. But, am i thinking in the right way? Would they become almost equally charged and would that happen almost immediately? Before the first of the surplus electrons flows thru the resistor? $\endgroup$ – Marty Mar 5 '17 at 15:35
  • $\begingroup$ When the electrons are moving from the charged conductor to the neutral conductor, some electrons will be moving from the neutral conductor to the ground simultaneously. $\endgroup$ – Yashas Mar 5 '17 at 15:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.