According to emf concept,we say that due to potential difference between electrodes of battery, electrons or charges want to move to opposite electrode. But electrodes are not joined. So they have to pass through wires. Wires act as a conducting path.

But here is contradiction, we often say that electrons in a circuit moves in random motion before potential difference is applied. And after p.d is applied they start moving.

So where do charges originate to flow? Is it in electrodes or in wires?

Please also tell why electrons in a circuit in in random motion and afterwards it starts straight moving?


A simple explanation would be:

  1. Charge doesn't originate from the voltage source. The voltage source creates a potential difference $\Delta V$ between its terminals and the wires, and this potential difference in turn creates an electric field $E= \frac {\Delta V}{d}$, associated with this electric field is an electric force that acts on the electrons in the wire $F= qE$. Since the wire is a conductor it has a lot of free electrons spanning its entire length, the electric force accelerates the electrons, and although the drift velocity of electrons is relatively very slow, the electrons collide creating a chain reaction of displacements throughout the wire. Moreover, this electron "communication" rate falls slightly short of the speed of light. This is analogous to pumping water out of a hose, the accumulative pressure of the water cause each infinitely small section of water to displace the infinitely small section in front of it which in turn causes the continuous flow we observe.

  2. As to why electrons move randomly in a wire when no voltage source is applied, this is from the nature of the electrons "movement" around the nucleus. However, the nature behind these movements has been ambiguous ever since quantum physics was founded, and all the nucleus orbit models were theoretically abandoned ( although still being taught at schools) , consequently being replaced with models that depend on an mathematical prediction of the motion/location majorly based on uncertainty and probability.

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