I'm a zoology minor and I'm trying to understand electrical gradient. I found this explanation in an authentic website but cannot undertand it fully.

An unequal distribution of charges across the membrane creates the electric potential difference. The electric potential difference creates the electric force acting on the charged particles. The charged particles will move in the way that until the some time the charges are balanced on both sides of the membrane. Therefore, now electric potential difference is zero and the charges are not moving.

I'm writing down my doubts anybody who can clarify them is most welcome.

  1. When charges are separated by a membrane such that one end develops +55mV and the other end -55mV there will be a movement of charges from +55mV to move towards -55mV until the potentials on both sides become 0. Is this correct?
  2. The movement of charged particles , is it due to development of an electric field?

Charges at rest move when a force is applied on them and this is due to Newton's laws.

Now to apply a force, we need a field, like electric/gravitational field. Each field acts upon certain measurable properties of a system, like gravitational on mass, electric on charge etc.

Now potential is just a fancy name of height in electromagnetism. I hope you're familiar with gravity in your day to day experiences, now, let's take a look more carefully as to how is gravity applying a force on you, it takes you from a higher height to a lower height on earth. This height is gravitational potential.

Similarly, there is an electrostatic potential, it tells you that electrostatic force will take you from a higher electrostatic height to a lower electrostatic height, but since electrostatic force isn't always attractive, it can take you from a lower height to a higher height as well.

So, first comes electrostatic force and then comes potential, kind of like without gravity, you don't know what is high and what is low. You associate tallness of something as to how much effort you'll have to apply to climb it up.

So, now the answer to your question.

$2$. The movement of charge is indeed due to an electric field, but no charge will experience a force due to its own electric field, so you feel a force only due to the other charge. This is just how we've found stuff to work till now.

$1$. Both the charges feel the force due to other one and will come to the centre, kind of if we both stand on a frictionless surface and if I pull you and you pull me at the same time, we both meet at the centre.

Also, you're used to thinking of height from a flat earth's perspective. For example, on earth actually, things that are on the same concentric sphere w.r.t. earth's centres are actually at same height, since it will take equal amount of work to reach all those points. So, think of height as how much work you'll have to do against the field force to reach that point. More the work, more the height.

  • $\begingroup$ Thank you. But what I have asked in the 1st question is that correct? $\endgroup$ – Tyto alba Jun 9 '16 at 9:57
  • $\begingroup$ No, it isn't. They both will meet at the centre or somewhere in between and then potential will be 0 everywhere as the charges are equal. I'd request you to try to relearn what potential, I know a lot of literature doesn't explain it clearly, but try thinking about gravitational potential first. $\endgroup$ – Isomorphic Jun 9 '16 at 10:57
  • $\begingroup$ gravitational yhea, they meet in between, that is if +,- are both mobile and compatible. in ionic system, they do many things, meet in between and meet at the surface of plates. But if we got to discuss electic current only, its the electrons being affected by field. $\endgroup$ – Jones G Jun 9 '16 at 11:22

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