Current Flow

[Besoeker]

Or less restriction (resistance, impedance).

I'd say bigger pipes, but the the analogy fails in that larger wires will not give an equivalent increase in flow to the analogy of larger pipes... unless you include some type of utilization equipment which provides essentially the same analogous restriction to flow.

More voltage (pressure) generally results in more current (flow).
That's what the simple and direct analogy is about.

But if you want to complicate it.......

 

[jeremysterling]

NOTE TO THE PHYSICS MAJORS: Let's please not confuse the OP with any true stories...

I was doing alright with series circuits until a thread about source impedance made my head hurt.

 

[mivey]

NOTE TO THE PHYSICS MAJORS: Let's please not confuse the OP with any true stories of drift current and the way current really behaves. Let's keep things simple, until the OP is ready to go deeper into the theories of our industry. It is not a bad start to think of current as though it were cars going around a race track. We know that that is not the truth, but it works as a first lesson in electrical theory.

I have said it before and I'll say it again: there is no reason to teach incorrect fundamental electrical theory. They have found it hurts students later. Even children's programs have been changed to teach electrical fundamentals correctly (but unfortunately not all) so we should expect no less from the adults.

Rant off.

 

[Sahib]

I am really having hard time when it comes to the flow of current in electrical wiring diagrams. I cant seem to grasp this current flow. Would highly appreciate if one could assist me in this regard.
Regards

The current as marked in the electrical wiring diagrams is called conventional current opposite to actual flow of electrons constituting the current. It was adopted long before the electrons were discovered. Rules such as left and right hand rules were based on conventional current flow direction and so it does not seem to be practicable to change to electron flow direction as current direction. Yet I think I saw Mikeholt use electron flow direction as current direction in his text books. Perhaps he adopted B.Franklin's practice.

 

[charlie b]

. . . there is no reason to teach incorrect fundamental electrical theory. They have found it hurts students later.

I am not advocating teaching incorrect theory. Rather, I am advocating telling the students that the theory is quite complex, that you are going to give them a simplified version to start with, that they should be aware that the simplified version does not represent the entire story, and that they should look forward to learning more of the in depth theory as they advance in their careers. You might even let them know, as you present the simplified version, which parts of the simplified version are going to be presented in more complex lessons later on. For example, you might tell them that you are going to treat current as though individual electrons make the full trip around the circuit at nearly the speed of light, and therefore make that trip many, many times in the same direction before, in the other half cycle, they start travelling in the opposite direction and make that reverse trip many, many times. Your intent here would be to provide an understanding of AC versus DC current. The nature of drift velocity can be briefly mentioned, but only briefly so as not to take attention away from the intent if this lesson.

 

[Smart $]

I am not advocating teaching incorrect theory. Rather, I am advocating telling the students that the theory is quite complex, that you are going to give them a simplified version to start with, that they should be aware that the simplified version does not represent the entire story, and that they should look forward to learning more of the in depth theory as they advance in their careers. You might even let them know, as you present the simplified version, which parts of the simplified version are going to be presented in more complex lessons later on. For example, you might tell them that you are going to treat current as though individual electrons make the full trip around the circuit at nearly the speed of light, and therefore make that trip many, many times in the same direction before, in the other half cycle, they start travelling in the opposite direction and make that reverse trip many, many times. Your intent here would be to provide an understanding of AC versus DC current. The nature of drift velocity can be briefly mentioned, but only briefly so as not to take attention away from the intent if this lesson.

I don't think it is that hard to understand that we actually need to teach a simplified version. I can think of many perceptually analogous scenarios to use for comparison. Waiting until later___IMO___doesn't make it harder to understand; it makes it harder to accept, because they were taught something different.

 

[mivey]

I am not advocating teaching incorrect theory. Rather, I am advocating telling the students that the theory is quite complex, that you are going to give them a simplified version to start with, that they should be aware that the simplified version does not represent the entire story, and that they should look forward to learning more of the in depth theory as they advance in their careers. You might even let them know, as you present the simplified version, which parts of the simplified version are going to be presented in more complex lessons later on. For example, you might tell them that you are going to treat current as though individual electrons make the full trip around the circuit at nearly the speed of light, and therefore make that trip many, many times in the same direction before, in the other half cycle, they start travelling in the opposite direction and make that reverse trip many, many times. Your intent here would be to provide an understanding of AC versus DC current. The nature of drift velocity can be briefly mentioned, but only briefly so as not to take attention away from the intent if this lesson.

Simplification is absolutely needed. Rome wasn't built in a day.

The problem becomes simplifying without destroying fundamental theory. Much effort has been put into developing lessons that don't require un-learning later. We want to lay building blocks that we can add to, not have to tear down to the foundation later. It would be worthwhile to study some of the lessons learned and how to make a better presentation of fundamentals without creating stumbling blocks. I have read quite a few of these papers and they are really fascinating. Wish I had time for more.

I guess what caused me concern was your statement about the current picking up more energy after running through the loop. This is akin to saying when I speak I shoot air molecules out of my mouth at some 700+ mph and they crash into your ear drum for you to hear. It might be a simple story of sound to a child. The problem is that it is not a simplification but a fundamentally flawed explanation. Same vein as saying water molecules travel at hundreds of mph and crash into the shore then return to the ocean to get more energy for the next wave.

It may seem harmless but I see too many times where people just struggle to get past those things once learned.

 

[Sahib]

I guess what caused me concern was your statement about the current picking up more energy after running through the loop.

But for the resistance of a conductor loop, no energy would be needed for the sustenance of DC current in the conductor. If AC current is involved, energy input would be needed because some of it is radiated into space from the conductor.

 

[GoldDigger]

But for the resistance of a conductor loop, no energy would be needed for the sustenance of DC current in the conductor. If AC current is involved, energy input would be needed because some of it is radiated into space from the conductor.

It is a smaller effect except at relativistic speeds, but DC will also radiate energy as the electrons turn the corners of the loop.

 

[Sahib]

It is a smaller effect except at relativistic speeds, but DC will also radiate energy as the electrons turn the corners of the loop.

It is reported that current induced in superconductor loops does not reduce in magnitude for a long time.

 

[Sahib]

DC will also radiate energy as the electrons turn the corners of the loop.

Interesting. I thought change in direction without change in speed of electrons motion does not radiate energy. Any reference?

 

[mivey]

But for the resistance of a conductor loop, no energy would be needed for the sustenance of DC current in the conductor. If AC current is involved, energy input would be needed because some of it is radiated into space from the conductor.

Completely off topic since we are not discussing a closed loop superconductor. Charlie's loop used regular wire and had a load in the loop.

The issue is treating the charge carriers as if they were like a bunch of coal cars picking up energy at the source and dumping it at the load. The load includes the end use load as well as the conductor resistance. But the charge carriers are not gradually spilling their loads along the track and dumping the coal at the end load as they make the turn. An analogy like that is fundamentally flawed and would have to be unlearned later.

 

[Sahib]

mivey:
You told in your post#27,'' current picking up more energy'' in relation to which I posted with the hope that it would provide more clarification to the OP.

 

[mivey]

mivey:
You told in your post#27,'' current picking up more energy'' in relation to which I posted with the hope that it would provide more clarification to the OP.

Doesn't matter as the whole concept was flawed from the beginning (see my previous post). IMO, adding in a superconductor with no end use load doesn't clarify but just adds a layer of complexity to the discussion. It is okay to consider the conductor resistance as negligible but we still need to include the end use load or we are off on a tangent discussion about superconductors and what not.

 

[GoldDigger]

Interesting. I thought change in direction without change in speed of electrons motion does not radiate energy. Any reference?

Any acceleration of a charge carrier, whether it changes the speed or not, will produce radiation.
Once you get to a high enough energy range you have to use linear accelerators instead of circular ones for electrons. Otherwise it would radiate as much energy on each lap as you put into it on each lap.

 

[ggunn]

You guys crack me up.

 

[Smart $]

...
NOTE TO THE PHYSICS MAJORS: Let's please not confuse the OP with any true stories of drift current and the way current really behaves. Let's keep things simple...

You guys crack me up.

Charlie's request was like asking pre-adolescents to not do something while you're away. :happyyes:

 

[Sahib]

mlvey:Well- Your aim is to convey the idea that during a current energy is transported through electromagnetic field. But that field is associated with electrons mass in the conductor per Einstein equation. So it does not seem contradictory to say electrons carry energy by increase in their mass. So charlie
anology seems about right.

 

[mivey]

mlvey:Well- Your aim is to convey the idea that during a current energy is transported through electromagnetic field. But that field is associated with electrons mass in the conductor per Einstein equation. So it does not seem contradictory to say electrons carry energy by increase in their mass. So charlie
anology seems about right.

I'm certainly not saying Charlie ever supported the idea of electrons carting the energy around. I'm just saying his analogy needs work so it can be a foundationally correct simplification.

The fact that you actually support the idea of electrons carting the energy around should be motivation enough.

 

[Sahib]

mivey:You foiled all my attempts on reconciliation. What is more you are not offering any improved version charlie analogy either.