# Voltage drop and voltage dividers

First, I'm not interested in numbers or the general math behind this. I know how to split voltage into some particular value(s). But what is actually going on?

I get Kirchoff's Voltage Law, or at least in terms of numbers. But how do the "electrons" know, where to drop which amount of energy?

Let's say I've got two 1000 ohm resistors in series and 6V DC source.

Well the voltage just between the resistors will be 3V, the electrons lost half of their energy.

If there were 3 of those resistors, it would be 2V.

This "voltage drop" is determined by "what is about to come" after the resistor.

How is that possible?

The resistors are always the same but they still "eat" different amount of volts based on the entire circuit, not just on themselves.

How do the "electrons" know how to distribute their energy?

• How water "knows" how to distribute it's pressure in split pipes? Right, it doesn't. There are fundamental physical laws governing it. How deeply you want to descend? Apr 8, 2019 at 16:49
• Electrons don't make decisions on their own, so to speak. It splits off because there are alternative paths that cause "leakage" in the main conduit (or bus, however you want to perceive it). If you cut a vegetable in half, you'll still have the same amount of vegetable but know you have two separate objects (plus some debris on the cutting utensil). Why do you have two separate objects? Existence is a complicated argument but it can be justified by our laws of the universe.
– user103380
Apr 8, 2019 at 16:56
• @EugeneSh. As deep as you'd like. Why does 1K resistor once "eats" 1V and sometimes 10V depending on the rest of the circuitry ? Apr 8, 2019 at 17:14
• You might read this or this to get a feel. But the gist is that very small numbers of electrons "stick" to the surface of the metal wiring, setting themselves very quickly in just such a way to "direct" the electron flow as it must. Electrons that make up the current drift along and cannot "see ahead" or "mind-read" the future. Instead, those few static charges set themselves up, as needed, very rapidly. Then the flow is directed by repulsion from those static charges on surfaces.
– jonk
Apr 8, 2019 at 19:57

An electric field is maintained by some power supply. Resistors in such a field move electrons around (according to Ohm's law). Heat results, and an energy-determining equation tells us how much heat power is produced.

No electron 'knows' anything except the local field that makes it drift through the resistor (which direction, what current density, is given by Ohm's law.). The voltage, the potential energy per unit of charge, is NOT A PROPERTY OF THE ELECTRON, it is associated with the position (the node in the circuit) at which a measurement can be made, and is determined by the electric field in ALL parts of the circuit (perhaps in all of three-dimensional space).

This "voltage drop" is determined by "what is about to come" after the resistor.

Except for arbitrary conventions in an oriented circuit diagram, there is no 'after' or 'before' a node of the circuit: a simple circuit takes on the same current in all parts, in a closed loop. Every part of the loop is 'before' and 'after' every other part. All the equations for the elements of the loop are solved simultaneously, none is 'first'.

Its not the electrons who know how to distribute their energy but its the load that tells electrons how to distribute the energy of electrons.

Suppose you are running and you have energy you got from food..

You pass through a hill. Then you pass through a desert and then you pass through the jungle.

And then all your energy is consumed. And you dropped your energy in hill desert and jungle and each of them took your energy according to them. That drop of energy is like voltage drop of electron.

Electron takes its energy from the battery and then the loads consume that energy.

Law of conservation of energy says that whatever energy electron has, it must be consumed by the load. If the load is big all energy will be consumed in a long time and thats what power is. Energy consumed in one second.

If the load is small all energy will be consumed in a very short time and thus we have more power in this case.

Without numbers this is all just hand waving, but ...

The energy in the electron is not changing. It has the same mass in all circuits and moves at the same speed. What changes is the number of them that are moving. One ampere is defined as blah blah time ten to the eighteenth electrons per second. The greater the impedance between the two terminals of a DC source, the fewer electrons move. Fewer electrons, less energy.

The water and pipe analogy doesn't work well in the details (for example, water molecules do move faster and slower with pressure changes), but it does this part pretty well. The greater the restriction is a pipe section (smaller diameter equals higher resistance), the greater the pressure drop (pressure differential equals voltage differential) across the section. Thus, when a larger resistor is in series with a small resistor, a larger percentage of the total voltage is across the larger resistor.

• No, the energy of the electron is changing. This is just wrong. Apr 27, 2020 at 13:59