Voltage vs Current. A cause or a consequence?

Thread Starter

Raúl Figueirinha

Joined Nov 13, 2020
1
Is it the potential difference that creates the current or is it the current that creates the potential difference?

This maybe sounds basic but that’s exactly why it’s so important

Thank you
 

SamR

Joined Mar 19, 2019
3,484
I'd vote for potential even though it's a bit of a chicken or egg question... Without potential, there is no current flow.
 

AlbertHall

Joined Jun 4, 2014
11,498
Yes, it's all a matter of how you look at it.
The secondary of a current transformer wants to drive a fixed current through whatever you connect to it, so this is more like a current producing a potential across its load impedance.
 

andrewmm

Joined Feb 25, 2011
1,751
Is it the potential difference that creates the current or is it the current that creates the potential difference?

This maybe sounds basic but that’s exactly why it’s so important

Thank you

yes

same question as

does a clock go
tick tok
or
tok tick

You can't have a current without a voltage.

In theory you can have a voltage without a current, but you cant measure the voltage with out a current,
so its a mute point.
 

andrewmm

Joined Feb 25, 2011
1,751
How does the gold leaf move ?
Charge moves from one source to another, charge moving is a current,
Ok, not much of one, but still a current.
 

LvW

Joined Jun 13, 2013
1,299
It doesn't once charged... Chicken? or Egg?
I am sure that it is NOT a chicken-egg problem.
What is the thing we call "current"?
Current is the movement of charges. Why do they move?
Because there is an E-field within the conducting material which forces/allows the charges to move.
Hence, no current without a driving voltage which is the cause for the E-field.
A current never can cause the voltage which is needed to enable this current.

HOWEVER - during circuit analyses and synthesis we are allowed to assume that a current can produce a voltage - and that`s what we are doing all the time. This is possible because - from the mathematical point of view - Ohms law in its original form (R=V/I) can also be written and interpreted in the form V=I*R.
But this must not be seen as a proof for V being the result of I.
 

SamR

Joined Mar 19, 2019
3,484
You can't get V without I as in you can't get chickens without eggs and versa visa... It's all a matter of perspective the same as GND.
 

LvW

Joined Jun 13, 2013
1,299
You can't get V without I as in you can't get chickens without eggs and versa visa... It's all a matter of perspective the same as GND.
I dont think that physical laws are a "matter of perspective".
With very few exceptions (natural physical laws like gravitation etc.) all observable physical effects have one single cause .
 

crutschow

Joined Mar 14, 2008
27,704
Typically it's viewed as a potential difference causes the current.
It's a voltage source that provides the energy to keep the current flowing in the circuit impedance.
Of course, in a superconductor, you can have a current without a voltage.
So I think the question borders on the philosophical.
 

andrewmm

Joined Feb 25, 2011
1,751
You can't get V without I as in you can't get chickens without eggs and versa visa... It's all a matter of perspective the same as GND.

Thank you SamR,

I think we are in agreement,
V can exist without a charge flow, as in capacitor,
but to measure V , you need a charge to flow, i.e. a current...
 

AlbertHall

Joined Jun 4, 2014
11,498
Thank you SamR,

I think we are in agreement,
V can exist without a charge flow, as in capacitor,
but to measure V , you need a charge to flow, i.e. a current...
A voltage (a real world voltage) cannot exist without current flow as any physical thing will have capacitance and there can be no voltage until current has flowed to charge that capacitance.
 

crutschow

Joined Mar 14, 2008
27,704
to measure V , you need a charge to flow, i.e. a current...
In practice you can make that current negligible by using a MOSFET circuit, or a null type circuit (adjust an external voltage until there is zero current flowing into the voltage being measured.
any physical thing will have capacitance and there can be no voltage until current has flowed to charge that capacitance.
Of course there is that initial transient.
But in the steady state there can be voltage without current.
 

andrewmm

Joined Feb 25, 2011
1,751
In practice you can make that current negligible by using a MOSFET circuit, or a null type circuit (adjust an external voltage until there is zero current flowing into the voltage being measured.
Of course there is that initial transient.
But in the steady state there can be voltage without current.
@crutschow
I think we are in agreement,
you need a charge to flow to measure a voltage , even if that is small.
and in the stead state , no current flows, but you have a voltage, as in a charged perfect capacitor,
but to measure the voltage ,you need a current to have flown.
 

LvW

Joined Jun 13, 2013
1,299
A voltage (a real world voltage) cannot exist without current flow as any physical thing will have capacitance and there can be no voltage until current has flowed to charge that capacitance.
OK - the problem really is if that is the question the OP had in his mind....I dont think so.
Of course, we can discuss if the slow discharging process of a battery is something like current - but I think, the core of the question is the following:
We have - as an example - a voltage divider (R1 and R2) and driving voltage V.
The current will be V/(R1+R2) .
Now, the voltage across R2 is certainly V2=I*R2.
Does this mean that the current I is the cause of V2?
My answer: Of course NOT!
For calculating purposes we can assume that the current I produces the voltage V2 - but physically spoken this is not true!
It is, of course, the voltage V across the series connection of both resistors that allows the current I. And the E-field caused by V is divided between both resistors according to their individual conductivity.
 

nsaspook

Joined Aug 27, 2009
8,657
Is it the potential difference that creates the current or is it the current that creates the potential difference?

This maybe sounds basic but that’s exactly why it’s so important

Thank you
In circuit theory we normally use voltage potential because it's easy and intuitive to use as it's very similar to other simplified physical forces in concept.

Fundamentally there is only one electromagnetic force. Separate voltage and current is a mathematical and symbolic simplification for circuit theory that assumes an instantaneous cause and effect for two separate forces that can be easily measured with simple instruments. At the small distances and time periods (quasi-static) normally expected at the beginning student level instantaneous cause and effect is a good approximation but falls flat (Kirchhoff's fails, Faraday's law remains true) as soon as there is non-conservative time-dependent flux (induction). This about the point where you will need to change the mental idea of separate voltage/current cause and effect into a em field mental picture where you can look at the single entity representation of electrical energy with time and space relative views that range from the electric to the magnetic for an observer as needed.

 
Last edited:

GetDeviceInfo

Joined Jun 7, 2009
1,875
Is it the potential difference that creates the current or is it the current that creates the potential difference?

This maybe sounds basic but that’s exactly why it’s so important

Thank you
It’s neither. Voltage and current are the products of electrical energy being introduced into an electrical circuit. Those products are shaped by the circuits characteristics.
 
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