I referred to this question potential difference but had a few doubts as to why do electrons move in a circuit? What exactly causes them to do so? And what is the chemical reaction in the cell which causes the electrons to move back to the higher potential difference? Why do the electrons move back to the higher potential difference? Sorry for these many questions and I would be more than happy to find them answered...


1 Answer 1


I'll go with your all questions one by one:-

Applying a potential difference across the ends of a conductor creates a uniform electric field inside the conductor, if you are aware of the forces which takes part in the electrodynamics such as coulombic forces, electromagnetic forces etc. (I'll assume that you are aware about these terms if not, then you can find the complete information about the terms here and here) So, this electric field inside the conductor exerts a force on all the charges inside the conductor which we call it as an electric force or Coulomb force but because only the free electrons has the ability to move so only those charges will take part in forming the electricity.

The amount of Electric force exerted by an external electric field on some charge $q$ is given by:-

$\vec{F} = q\vec{E}$

So the answer to your question that why only electrons moves is that the answer is pretty much simple i.e electrons have mobility and positive charges do not. (I meant positive charges as vacancies here ) only the $FREE$ electrons inside have the ability to move freely anywhere (But in the case in which the potential difference is applied by a battery or some power source, the direction of motion of all the free electrons will become the same which will head towards the positive potential of the battery) (in case of semiconductors and electrolytes the cases are pretty much different). We consider that instead of assuming negative charges or electrons are moving, we assume that the positive charges are moving $BUT$ in the opposite direction in which electrons or negative charges moves which we call it as conventional current.

So back to the above equation, in this case the charge $q$ is an electron and the electric field formed inside the conductor will be directed form the higher potential to the lower potential and with this, the negatively charged particle experience the force opposite to the direction of an electric field.

$\vec{F} = e\vec{E}$

So as we can see that, under the influence of an external electric field created by the battery the electrons will experience this much amount of force individually. And that will make it move, but wait! You might be thinking that if there is the force then there might also be the acceleration which will cause the electrons to accelerate? You are assuming it correctly, but this phenomenon does not happens here because there are not only free electrons inside the conductor but also the other atoms and vacancies which are making the conductor electrically neutral. If they are present then they might become an obstruction which always tries to disturb the motion of the electrons and these obstructions inside the conductor, we call it as the resistance of the conductor and if the electrons get accelerated from the initial velocity then after the collisions either they will loose their energy in the form of heat or get deflected from the direction in which they should actually move. And the velocities of the all electrons can't be studied very closely so scientists have introduced the term $\textbf{drift velocity}$ to consider an average velocity at which all the electrons can be considered as moving at this constant velocity or speed at which electricity moves.

And for the question that what happens inside a battery, you can have a look at this chemistry stackexchange article here because this topic much more belongs to the branch electrochemistry.

And I've covered the part which is considered on-topic here.

Hope it helps!

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    $\begingroup$ From where do the free electrons result from, shouldn't they be attached to an electrovalent compound instead if being free in the surroundings? Shouldn't they be permanently attracted to the positive particles? $\endgroup$ Jan 25, 2022 at 13:36
  • $\begingroup$ Yes they do attract the negatively charged particle towards their vacancies but let's consider an example of copper which has the atomic number 29 and has electron configuration of $1s^2$ $2 s^2$ $2p^6$ $3s^2$ $3p^6$ $4s^2$ $3d^9$ as we can see that because of this huge amount of electrons are inside a copper atoms so we can say that it has a very large atomic radius and ionization energy is inversely proportional to the atomic radius that means if an atom has a larger radius the smaller the ionization energy required to pull out the electrons from the outermost shell....... $\endgroup$ Jan 25, 2022 at 14:16
  • $\begingroup$ ......So because of this small amount of energy is required to pull out the loosely attached electron, so the temperature difference between the surroundings and the conductor cause transfer of heat energy and this much small amount of energy is sufficient for the electrons to get out of the shell and even if it is attracted again, it's going to loose the electron until and unless there is some temperature difference between room and the conductor and the cycle goes on...I hope it's all clear to you now $\endgroup$ Jan 25, 2022 at 14:21
  • $\begingroup$ Moreover I'm going to say that If that electron gets the energy more than enough the amount of energy required to get it ionized then the remaining amount of energy will get converted into the kinetic energy and that why it's often said that, even if the conductor don't have any potential difference across its ends electrons are still moving inside the conductor but because they move in a random direction then we count its average velocity to be zero and hence the current remains zero. $\endgroup$ Jan 25, 2022 at 14:28
  • $\begingroup$ What causes the electrons to move and why does the movement itself creates current? And Thanks a lot for the detailed answer and comment. $\endgroup$ Jan 26, 2022 at 7:47

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