# How does a current "know" where to go

• xWaldorf
In summary: This is how Ohm's law works, electrons follow electrical fields. Electrons don't know anything, they just go where forces on them take them and when there's less in the way, more go in that direction. This is how Ohm's law works, electrons follow electrical fields.
thetrellan said:
Actually Ohm's law helps us measure resistance.
? It relates to Resistance. Your statement is the equivalent of saying Speed helps us measure Speed.
Resistance is just a Ratio which may or may not remain constant, depending on the conductor involved. Ohm's Law is only followed by metals at constant temperature. Non-Ohmic components exist and you can still measure V and I.

all the material have a different current conductivity. so the current will go to material that have the haigh current conductivity. example : 2 material /// man and steal . the current will go to steal

weirdoguy and sophiecentaur
rephael said:
all the material have a different current conductivity. so the current will go to material that have the haigh current conductivity. example : 2 material /// man and steal . the current will go to steal
Again: false.

Current will go through both. to varying degrees, depending on their resistance.

DaveE and sophiecentaur
tech99 said:
I usually think in terms of the initial surge at switch-on.
I don't think you meant that . You would only need to think of that when looking at a change. We launch into the simple basic DC calculations first and often we think no further except when there's a PF post, a smartypants Exam question to answer or when we're dealing with very minority situations where the warning light in our brain has been lit.
I could be wrong about this and you may be a designer of Time Domain Reflectometers or a power systems analyst.

jbriggs444
sophiecentaur said:
I don't think you meant that . You would only need to think of that when looking at a change. We launch into the simple basic DC calculations first and often we think no further except when there's a PF post, a smartypants Exam question to answer or when we're dealing with very minority situations where the warning light in our brain has been lit.
I could be wrong about this and you may be a designer of Time Domain Reflectometers or a power systems analyst.
I like to think of it in terms of an equilibrium and relaxation toward a stable equilibrium.

As long as one is dealing with typical passive components, the possibility of more than a single equilibrium state does not arise. If there is an equilibrium state, it will be approached.

sophiecentaur said:
I don't think you meant that . You would only need to think of that when looking at a change. We launch into the simple basic DC calculations first and often we think no further except when there's a PF post, a smartypants Exam question to answer or when we're dealing with very minority situations where the warning light in our brain has been lit.
I could be wrong about this and you may be a designer of Time Domain Reflectometers or a power systems analyst.
Exactly; the question of how does the current know where to go comes up here perennially for some reason.

tech99 said:
for some reason.
The reason is that Electricity is Hard. I never know why people try to tell us otherwise.

etotheipi and weirdoguy
tech99 said:
Exactly; the question of how does the current know where to go comes up here perennially for some reason.
Humans tend to anthropomorphize electrons because we appear to control, generate and manipulate electrons and EMF. Ascribing human attributes to things aids acceptance, reduces fear and eventually promotes rational understanding.

Electrons become the 'familiars' of our technology 'wizards'.

We name large storm systems. We describe pandemics with emotional terms.

sophiecentaur
xWaldorf said:
how does the current "knows" to flow towards the around the resistor?
The usual model of current is that it is an aggregation of electrons. So you need to ask how an individual electron "knows" which way to go. If you are in a stream of people leaving a building that has 2 exit doors, the exit you take is probably influenced by the behavior of people near you. I don't know anyone has modeled current flow to a level of detail that shows the behavior of individual electrons moving as a crowd. Your question seems to ask for that level of detail.

Stephen Tashi said:
The usual model of current is that it is an aggregation of electrons. So you need to ask how an individual electron "knows" which way to go. If you are in a stream of people leaving a building that has 2 exit doors, the exit you take is probably influenced by the behavior of people near you. I don't know anyone has modeled current flow to a level of detail that shows the behavior of individual electrons moving as a crowd. Your question seems to ask for that level of detail.
I think that is an example of partition noise.

Stephen Tashi said:
The usual model of current is that it is an aggregation of electrons. So you need to ask how an individual electron "knows" which way to go. If you are in a stream of people leaving a building that has 2 exit doors, the exit you take is probably influenced by the behavior of people near you. I don't know anyone has modeled current flow to a level of detail that shows the behavior of individual electrons moving as a crowd. Your question seems to ask for that level of detail.
I think this is valid/true. The wording of the OP implies to me that he doesn't recognize that the wires are already filled with electrons prior to turning on the circuit. It's as if he thinks the electrons would wander down the wire until they get to to the resistor, then turn around and go back the other way after finding out it is in the way. It's equivalent to standing by yourself in a lobby with two doors and not knowing which one is locked and which isn't. If instead you have a line of people that is moving fast through one door while a bunch of people are pushing in vain on a locked door next to them, it becomes obvious why you go through the open door. You don't even have to "know" anything; you could close your eyes and let the crowd push you through the open door.

jbriggs444
russ_watters said:
It's equivalent to standing by yourself in a lobby with two doors
... and then Monty Hall says, "wait! what if I open this door..."

Sorry , now back to the thread...

hutchphd and etotheipi

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