# Problem with self-inductance

1. Jul 23, 2008

### ascii

I have a problem with the concept here. Does it mean that the flux of a magnetic field is function of a field which is function of a current which by itself is function of that flux?

Last edited: Jul 23, 2008
2. Jul 23, 2008

### Staff: Mentor

3. Jul 23, 2008

### ascii

Yeah I was trying that myself but there were some problems with the database, so I just wrote what I wanted to say, with words.
I don't know if you want me to be more detailed now or that post was before you saw my edit.

4. Jul 23, 2008

### Staff: Mentor

The current in a coil creates a flux, and changes in the flux create a back EMF that opposes the original current. So yes, the current and flux are affecting each other simultaneously, and stabilize at AC values that depend on the self-inductance value.

5. Jul 23, 2008

### ascii

Alright, thanks.
Now something else.
My book multiplies the time variation of the magnetic flux with the number of loops, and says that value negative is what equals to the induced EMF.
I wonder, isn't the number of loops already considered in the flux integral?

6. Jul 23, 2008

### Staff: Mentor

I'm going to move this thread to the Homework Help section of the PF, since it is for homework/coursework.

I'm not sure I understand your question, but you get the flux from Ampere's law, and the resulting back-EMF from

$$V = -N \frac{d\phi}{dt}$$

7. Jul 23, 2008

### ascii

Then I don't understand what is that other part of the forum for
Anyway...
Ampere's law says that the integral of a magnetic field around a closed loop equals mu zero times the current penetrating a random surface attached to that loop.
What you wrote there is Faraday's law. But that aside, I don't understand why would you write that factor N. What does it mean? And again, if it is the number of loops, isn't that already considered in the integral of the magnetic flux?

8. Jul 23, 2008

### ascii

Alright I get it now, it's not considered in the integral because you do it over the transversal area of the coil.

9. Jul 23, 2008

### Staff: Mentor

Oops. I said I was going to move the thread, and then spaced it as I answered the questions. Sigh. I'll move it now.

BTW, the Homework Help area of the PF is for homework and coursework type questions. There are special rules in those forums, to help in the tutorial nature of the help that can be provided. Check out the "Rules" link at the top of this page for more clarification.

Welcome to the PF!