# Flux Density in Mutual Induction Solenoid with Core

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1. Jul 12, 2016

### entity314

For a standard solenoid, I've found that
B=μnI
where
n = number of coils
I = current

Firstly, is the permeability of soft iron 0.08, as I found?

Primarily, however, I'm wanting to know if this still applies for a mutual induction apparatus like in
https://www.scientrific.com.au/PDFs/em2220-001.pdf

2. Jul 12, 2016

### Replusz

I think B=μnI/l where l is the length of the solenoid.

3. Jul 22, 2016

### leright

Keep in mind that nothing interesting will happen with DC currents. Yes, a magnetic field will be generated but you will not get any mutual induction unless your flux is changing (i.e. varying current through one of the coils.

4. Jul 25, 2016

### entity314

It's for an alternating current.
Presumably the maximum flux density will occur at the current peak?

5. Jul 25, 2016

### Replusz

Yes, because
f7c6a5d2ff27b8dae2e9aa5657aa5909a8bc6d8e (sorry, click on the link, I couldn't copy-paste the formula)
and here B is a linear function of the current (I) as I wrote in my first post.
hth

6. Jul 25, 2016

### entity314

Thanks, that's what I though :)
Is the formula for the flux a solenoid correct though?

7. Jul 25, 2016

### Replusz

You mean this: B=μnI/l ?

8. Jul 25, 2016

### Replusz

It is correct assuming the solenoids length is much longer than the radius. B can be considered almost homogeneous inside the solenoid.
But in any case B is linearly proportional to I.
hth