electric-circuitselectric-currentelectrical-resistancepotentialvoltage
I need to know the underlying physics of what exactly happens different with the electric field in the resistor than in superconducting wires.
Why is it that when I connect a resistor, potential drops across its (resistor's) ends? Sorry for the silly question but I can't figure it out. I do know, energy will be dissipated and hence the voltage will drop but I'm looking for a more insightful and detailed answer.
The answer is simple, the resistor doesn't know what voltage drop to provide, and to some extent it doesn't "care" either (unless it's so high that the current fries it but that's another issue).
The "voltage drop" is only governed by the potential difference created by the generator (battery or other). If the circuit is open, the electrons have no path so there is no flow. As soon as the circuit is closed, the electrons have a path and start to flow across the conductor (a resistor is also a conductor).
The only thing the resistor will govern, is how strong the flow of electron will be from A to B (from one potential to another, but remember this potential was created by the generator, the resistor doesn't need to know it).
I often do the analogy between electricity and hydraulic flow. Consider the difference of potential (the voltage) created by the generator as a height, and the resistor as a slope. The flow of water will be different in the same way as the electrons in a circuit.
Consider the 3 scenario in the following image:
A:
No resistor to close the circuit => no current flow possible.B:
Low resistor. The electrons (or the water) fall from the high potential to the low one (rather rapidly).C: The electrons (or the water) fall from high to low potential, still from the same height (your Voltage drop is identical). Except this time the higher resistance (flatter slope) makes it harder to reach the low potential (=> lower current).Now imagine the high potential is 24V, or even 10,000, the mechanics are still the same, the electrons will flow from one potential to another as soon as they have a path, regardless of the resistor value. The only difference made by the resistor is how strong they will flow (how strong the current will be).
note: The analogies with the water flow are easily arguable and quickly reach their limits with complex circuits, this is not the exercise here. They still are a great way to explain electric current in the simple cases
The starting point of this question makes it hard to give a short, satisfying answer; maybe someone will come along and do a standout one with diagrams, but I don't have time for it. So I'll kick off with this:
With two resistors in series, there's more total resistance on the circuit, which means that less current flows. With less current flow, a given resistor drops less voltage because V=IR. Voltage drop isn't an intrinsic property of the resistor; resistance is.
Best Answer
Electric potential is a potential energy just like gravitational potential energy or indeed any other form of potential energy. Specifically, moving one coulomb of charge through an electrical potential of one volt produces (or requires) 1 joule of energy. From your question I guess you're basically happy with this, so the question is really how this energy is dissipated i.e. what happens to that 1 joule of energy?
When you apply a voltage to the conductor you produce a force on the conduction electrons so they accelerate - the potential energy is turned into kinetic energy of the electrons. However conductors are made up from a crystal lattice of atoms/molecules that is randomly vibrating due to thermal energy, and there is a probability that the moving electrons will scatter off this lattice and transfer energy to it. So the electron is slowed down and the magnitude of the lattice vibrations is increased. Increased lattice vibrations mean the conductor is hotter, so the kinetic energy of the electrons has been transferred into thermal energy in the conductor.
And that's what happens to the 1 joule of energy. It's transferred to the conductor and ends up as heat.
Some related issues you might want to look into further: when you cool a conductor you reduce the magnitude of the lattice vibrations and you make it less likely the electron will scatter off the lattice. That's why resistance (usually) decreases with decreasing temperature. The superconducting transition prevents electrons from scattering off the lattice, so they can't transfer energy to it and that's why superconductors have a resistance of zero.