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Pogba
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So what's the smplest illustration for voltage ,current and resistance and what's ohms law ?
Simon Bridge said:you said you had "voltage confusion"
CraigHB said:One problem that can be confusing is the formula on paper fails to point out that voltage has to be there first for current to flow. People sometimes make the mistake of assuming a voltage is present simply because IR says it should be there.
anorlunda said:It is also perfectly valid to say "voltage is present simply because IR says it should be there". If you prefer, think of a resistor connected to an ideal current source. The voltage appears because the current flows (and the current flows because the voltage appears). No first and second, but simultaneously.
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If you really want to find out what happens first, then you need time domain solutions to Maxwell's equations, but then that it no longer circuit analysis. You will find that the fields propagate at near light speed.
anorlunda said:If you really want to find out what happens first, then you need time domain solutions to Maxwell's equations, but then that it no longer circuit analysis. You will find that the fields propagate at near light speed.
You'd agree that Maxwell's equations describe your physical point of view? If so, then voltage does not come before current or vice versa - there's no causal relationship between them.LvW said:However, from the physical point of view it is clear that no current can exist without driving voltage - hence, voltage first and current next.
LvW said:However, from the physical point of view it is clear that no current can exist without driving voltage - hence, voltage first and current next. This basic rule applies, of course, also to circuits with "current sources" which, in reality, always are voltage sources eqipped with a very large (dynamic) source resistance.
OK - I must admit that I didn`t express myself clear enough. It was not correct to say "voltage first and current next" because this involves a time sequence.milesyoung said:You'd agree that Maxwell's equations describe your physical point of view? If so, then voltage does not come before current or vice versa - there's no causal relationship between them.
@LvW, can you give an example of something you'd consider a voltage source? A battery perhaps, do you consider that a voltage source?
Okay, let's use this as a starting point. In the following, in the questions I might pose, I'm not trying to trick you or anything, I genuinely just want to present you an alternative viewpoint. Your line of reasoning is shared by many.LvW said:... I would consider a battery as a (of course non-ideal) voltage source.
I'm not interested either in a discussion on the specifics of batteries, but it's one of the simplest examples I could think of of something you associate with a voltage source.LvW said:milesyoung - I am not sure if it makes much sense to discuss here the properties of a battery.
milesyoung said:... I gave you a 2-terminal black box with a battery inside and asked you to probe the terminals, what would make you conclude that it's a voltage source?
Sure, but that would also be the case for a nonideal current source.LvW said:Any electrostatic measurement device would react upon the potential difference, would it not?
milesyoung said:Sure, but that would also be the case for a nonideal current source.
Why is my black box not part of your reality?LvW said:Yes - because each non-ideal current source is (in reality) a non-ideal voltage source.
The force can be either electric or magnetic, depending on your choice of reference frame. I assume you're analyzing this from the rest frame of the conductor, but that frame is no more fundamental than any other.LvW said:Remember: Which effect (which force) causes the charges to move (forming the quantity we call "current") ?
I think, this can be answered only by means of an example for a technical realization of that what we call "current source".Averagesupernova said:Is a current source considered exotic by those who are only able to hook a voltmeter and simple loads to a voltage source?
sophiecentaur said:The OP has not shown himself since the top of the thread. Perhaps Pogba could respond and tell us
1. What he/she already knows about the topic
2. His/her views on what has been written already.
There is no such example in the real world. This is why I brought up super conductors since they are as close to ideal as we can get in the real world. No voltage, yet we have circulating currents. Maybe this drags the discussion in a different direction. Just thought I would throw it out there.LvW said:I think, this can be answered only by means of an example for a technical realization of that what we call "current source".
Where is such an example?
We are talking 'real world' and not mathematics.Averagesupernova said:There is no such example in the real world.
Averagesupernova said:Doesn't the discussion come down to can we have a circulating current with no voltage? Is there not current in a copper pipe when we drop a magnet through it? In the real world there is a finite resistance in the copper. What about a super conducting pipe?
https://en.wikipedia.org/wiki/Drude_model#Accuracy_of_the_model said:Historically, the Drude formula was first derived in an incorrect way, namely by assuming that the charge carriers form an ideal gas. It is now known that they follow Fermi–Dirac distribution and have appreciable interactions, but amazingly, the result turns out to be the same as the Drude model because, as Lev Landauderived in 1957, a gas of interacting particles can be described by a system of almost non-interacting 'quasiparticles' that, in the case of electrons in a metal, can be well modeled by the Drude equation.
This simple classical Drude model provides a very good explanation of DC and AC conductivity in metals, the Hall effect, and thermal conductivity (due to electrons) in metals near room temperature. The model also explains the Wiedemann–Franz law of 1853. However, it greatly overestimates the electronic heat capacities of metals. In reality, metals and insulators have roughly the same heat capacity at room temperature. The model can be applied to positive (hole) charge carriers, as demonstrated by the Hall effect.
One note of trivia surrounding the theory is that in his original paper Drude made a conceptual error, estimating electrical conductivity to in fact be only half of what it classically should have been.
LvW said:In this context: Is there any real technical device which we call "current source" (labor slang), that is not energized by a voltage?
Hi Claude - is there really no E-field involved? Which force then allows the movement of charges which were set free by photons?cabraham said:A photodiode works very well as a constant current source. Light incident upon the device produces current.
Voltage, also known as electric potential difference, is the measure of the potential energy difference between two points in an electric circuit. It is measured in volts (V) and is represented by the symbol V.
Current is the flow of electric charge through a conductor. It is measured in amperes (A) and is represented by the symbol I. Current can be either direct (DC) or alternating (AC) depending on the type of electric circuit.
Resistance is the measure of opposition to the flow of electric current in a circuit. It is measured in ohms (Ω) and is represented by the symbol R. Resistance is affected by factors such as the type of material, length, and cross-sectional area of the conductor.
According to Ohm's Law, voltage is directly proportional to current and resistance. This means that as voltage increases, current increases as well, while resistance decreases. Similarly, as voltage decreases, current decreases and resistance increases.
Ohm's Law is widely used in various fields such as engineering, physics, and electronics. It is used to calculate the voltage, current, or resistance in a circuit, and can also be used to troubleshoot problems in electrical circuits. It is an essential concept in understanding the behavior of electricity in everyday life.