# Voltage source and current source

• PhysicsTest
In summary, voltage and current sources are ideal circuit elements that are used to simplify circuit models. They do not exist in real life as perfect sources and can be modeled as a perfect source with an associated internal resistance. The distinction between voltage and current sources comes down to whether the internal impedance is high or low relative to the circuit it is connected to. A voltage source provides voltage without restriction, while a current source provides current without limit. In an ideal situation, a current source can pump any amount of current into a resistor, while an ideal resistor has no restriction on the amount of voltage or current through it. However, in the real world, sources are somewhere between a voltage or current source and have limitations. For example, a solar cell can act
alan123hk said:
do electric fields appear first or magnetic fields appear first?
The solution gives them in phase for a plane wave. Near field can have either one early or late.

cabraham
LvW said:
However, the remaining question is:
Is the "moving charge" which builds up the voltage equal to the phenomenon we usually call "current"? For example, is the induced voltage in a generator the result of a current?
I doubt - and, therefore, I think that the sequence voltage-current is not a "chicken-egg" problem.
I am engaged in electronic engineering, so I am not familiar with electrical engineering and generators, but in my concept, the basic function of a generator is to convert mechanical energy into electrical energy. There are two ways of movement that can constitute this energy conversion. One method is to generate voltage when the coil moves in a fixed magnetic field, and the other method is to fix the coil and move an electromagnet or permanent magnet around the coil to make the coil generate voltage.

In the above two cases, the generator generates voltage, so voltage seems to be the first step in generating electricity. I think this is a perspective on this issue, so there is actually no need to definitely affirm or deny it. But I guess someone may continue to trace the source. They may say that the voltage generated by the generator involves the relative movement between the coil and the magnetic field. For example, when the coil moves, the free charge inside it also moves with the coil, so this free charge moving in the magnetic field feels the force and and then generates voltage and electricity. In addition, the magnetic field inside the generator, whether it is created by electromagnet or a permanent magnet, must also be generated by current or effective current, so it seems that it is again the moving charge or some form of effective current is the first to play a very important role before the voltage is generated. So the process of tracing the source does not seem to be easy to end.

Last edited:
sophiecentaur said:
The solution gives them in phase for a plane wave. Near field can have either one early or late.
Haha, this is something I didn't think of before.

But if I remember correctly, the near field does not seem to propagate energy. The energy it stores is limited to a local range, or decreases as the distance increases.

In other words, the antenna near field is only reactive power, unless it has the opportunity to transfer energy to other places through capacitive or inductive coupling.

Last edited:
sophiecentaur
anorlunda said:
You have to use Maxwell's Equations, or QED, to get the "real" answer. Circuit analysis, and thinking with circuits won't get you there.
No - I don`t think so. In this thread, we are discussing voltage and current sources (properties and definitions). Hence, the core of the question is: What is the commonly used definition for the phenomenon we call "current"? This question cannot be answered by Mr. Maxwell, can it?

alan123hk said:
For example, when the coil moves, the free charge inside it also moves with the coil, so this free charge moving in the magnetic field feels the force and and then generates voltage and electricity.
Thank you for your interesting contribution. Of course, I can understand what you mean.
However, the remaining question is: Is the free charge movement inside the coil identical to the phenomenon we normally call "current" (In the context of voltage vs. current sources) ?

alan123hk said:
unless it has the opportunity to transfer energy to other places through capacitive or inductive coupling.
For any transfer of Power, there has to be a Resistive component sneakin' in somewhere.

There will be some stored reactive energy to couple the rotor and stator like a transformer except with commutation on the rotor. This will be proportional to the voltage potential increasing with RPM and regulator current. But power only is transferred with a "conjugate impedance" load like a massive capacitor like a battery which also has series resistance or simply an equivalent load resistance. P(t) = V(t)*I(t)

TonyStewart said:
There will be some stored reactive energy to couple the rotor and stator like a transformer except with commutation on the rotor. This will be proportional to the voltage potential increasing with RPM and regulator current. But power only is transferred with a "conjugate impedance" load like a massive capacitor like a battery which also has series resistance or simply an equivalent load resistance. P(t) = V(t)*I(t)
Have you somehow posted this to the wrong thread?

I see no other mention of rotor or stator in any other post in this thread, a thread which has been dormant for more than 1 year.

Thanks, That's why I'm still just an "Electron" I must have responded to the hijack #37 on page 2 without noticing page 1

TonyStewart said:
Thanks, That's why I'm still just an "Electron" I must have responded to the hijack #37 on page 2 without noticing page 1
You can re-post that reply to the correct thread, or use the "Report" feature to ask a Mentor to do that.
(Edited)

Also, I notice that you often respond to some specific post in a thread, without referencing that specific post. The "Reply" feature is a very handy tool for making such a reference.

Your active participation here on PF is greatly appreciated and encouraged.

SammyS

Last edited:
TonyStewart

• Electrical Engineering
Replies
8
Views
883
• Electrical Engineering
Replies
68
Views
4K
• Electrical Engineering
Replies
19
Views
1K
• Electrical Engineering
Replies
7
Views
893
• Electrical Engineering
Replies
19
Views
3K
• Electrical Engineering
Replies
80
Views
3K
• Electrical Engineering
Replies
8
Views
803
• Electrical Engineering
Replies
10
Views
1K
• Electrical Engineering
Replies
4
Views
934
• Electrical Engineering
Replies
1
Views
850