Continue to Site

# How a closed core coil works?

Status
Not open for further replies.

#### Ariaana

##### New Member
Hello guys
I have an important question which could not find the answer yet, that is a about Electromagnet.
As Faraday's law when a coil passes trough a magnetic field or exposes to a various magnetic field, cutting the flux by coil will produce current in coil winding.
At a closed core coil or inducer, current passing trough first winding produces a magnetic flow in closed core and that magnetic flow will produces some current in the second coil as transformer/
My question is that when all magnetic flux flows through the closed core and nothing we have to pass through the second winding,(That is a closed core which does not let the flux going out the core), so how the second current wil produce?

he

all magnetic flux flows through the closed core and nothing we have to pass through the second winding,
But there is.
The flux flows through the core, but the associated magnetic field is seen by the secondary winding.

How is seen by that?

As Faraday's law the flux should be cut by winding???

Perhaps this will help.

But there is.
The flux flows through the core, but the associated magnetic field is seen by the secondary winding.
Yes sure you are alright because we see the current at secondary one, but the point is that is not match the Faraday;s law.

Perhaps this will help.

when you charge coil A a magnetic field will charge in the core and you will see the change in coil B, but once the coil A is charged and the core is polarized you will not see any more change in coil B since coil B will only show a change in the core and not the actual field there.

electromagnets work great with DC current but transformers only work with AC currents

Think of it like this:

Image a cross-section of the part of a coil passing through an opening in a magnetic core - eg. where it goes though the centre of a toroid transformer or whatever.

The magnetic field originates in the coil and form a circular pattern around it. Think of "lines of force" patterns.
As the current starts and increases, those lines of force - the magnetic energy that is being built up - must spread from the coil and in to the core.

That cannot happen without the energy / field line also passing through any other conductors in that same core opening.

Likewise as the current in the primary reduces, the it's field weakens and shrinks back towards the coil wires.

[/QUOTE]
Think of it like this:

Image a cross-section of the part of a coil passing through an opening in a magnetic core - eg. where it goes though the centre of a toroid transformer or whatever.

The magnetic field originates in the coil and form a circular pattern around it. Think of "lines of force" patterns.
As the current starts and increases, those lines of force - the magnetic energy that is being built up - must spread from the coil and in to the core.

That cannot happen without the energy / field line also passing through any other conductors in that same core opening.

Likewise as the current in the primary reduces, the it's field weakens and shrinks back towards the coil wires.
Thank you at first my friend to spending time for me, and i hope i could transfer my opinion to you with my poor English.
As i understand you mean that the magnetic flux flowing through closed core is resulted of, sum of circular field of each wire in the first coil, spreading in the core. Yes sure that is correct, think more about this point pls, that magnetic flux is produced and spread-ed into closed core by changing current in the first winding(A), but for the second coil(B) that flux does not have to spread out again around the coil B, and normally there around the second winding should not be any flux to produce current, do not forget that the core is closed so all the flux producing by first winding on coil A run inside the core just.

when you charge coil A a magnetic field will charge in the core and you will see the change in coil B, but once the coil A is charged and the core is polarized you will not see any more change in coil B since coil B will only show a change in the core and not the actual field there.

electromagnets work great with DC current but transformers only work with AC currents
Thank you Dr. but that is not my answer.

but for the second coil(B) that flux does not have to spread out again around the coil B,

But the varying field cannot spread from any one wire or coil to the core without also passing through all the other wires in that same core aperture!

Does it depend on the radios of the core? I mean the distance between two coil?

But the varying field cannot spread from any one wire or coil to the core without also passing through all the other wires in that same core aperture!
I have to accept it, but still i do not understand how these two coils relate to each other.
The fundamental of a transformer stands on two coils which is winded on each other, so the flux generated from one coil, could pass from the second one, but in such a way same as closed core with two coils separated, that is really complicated to understand that, how the flux from one coil passes through another coil!!??

Ariaana

Just from my personal experience, I would suggest that you stop trying to reconcile your ideas on the matter with the explanations that are given to you.

Blank your mind of previous concepts and then re read the article suggested by alec_t in post #5. Otherwise, you risk to spend the hell of time in a futile exercise. The drawing shown at the beggining is quite clear to support the explanation there.

Sometimes, starting afresh on something is the most productive attitude.

This was a topic that was hard for me at first too, i think the thing we are missing is that a magnetic field is not energy ...
a magnet field simply occurs because all the atoms are pointing in the same direction. A Perminate magnet works cos all the atoms are again pointing in the same direction and able to hold there cos they are so close, as a magnet gets weaker it is due to the atoms moving out of alignment

an electro magnet is different in the sense that they use different material so that the atoms are so loose that they spin(align) with little effort ... that is the reason that they form the magnetic field for an electromagnet... but when we take the electric current away the atoms are loose enough that they dont all stay in the same direction and the magnetic field breaks down and the electromagnet stops being a magnet.

so when we apply power to a coil we are using energy to spin(line up) the atoms .. this can be detected in the second coil by the energy spike, but once the atoms are aligned they dont move(spin) anymore and without motion there is no energy which why you wont detect any more power in the second coil
... oddly enough though when you take the power away from coil 1 the atoms move to their unaligned position ... this motion of unalignment can also be seen in coil 2, but instead of a power spike , you would see a power dip... below 0 volts even.

so now hook up the coil to the battery and a button ... and push the button really fast .... the meter will give lots of varied readings ... an interesting point though is that the meter will not only jump when we push the button and apply power, but also when we let go of the button and take the power away.

so in summary the coil cannot detect a magnetic field, only the changes in one

Last edited:
Status
Not open for further replies.