# Magnetic flux in spool.

## Homework Statement

The attached picture shows a spool coil on a iron core with an air gap measuring 2.5mm. The spool is coiled by 0.5mm2 with rho cu = 0.0175 Ωmm2 /m. The average winding diameter for the spool is 3.18cm.

Compute the magnetic flux in the spool. ## The Attempt at a Solution

Using the equation: phi = I * N / Rm, I still miss I, and I have no idea how to compute it. Rm is the reluctance which I can get from a B-H characteristic - if that applies to this problem.

My first questions are these I guess: Is this the correct formula? If yes, how to I compute I?

Any feedback and help is as always greatly appreciated. Thanks.

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rude man
Homework Helper
Gold Member
Your formula is fine but you need to use the correct reluctance.
You also need either the voltage or the current in the spool.

Hint: the reluctance of the air gap is >> reluctance of the rest of the core. Forget B-H of the core!

Your formula is fine but you need to use the correct reluctance.
You also need either the voltage or the current in the spool.

Hint: the reluctance of the air gap is >> reluctance of the rest of the core. Forget B-H of the core!
If I need the voltage or current, it would apprear it's missing from the problem - and I do apologize for that. But since you say I can use the voltage, how should I go about it if we set the voltage to 24V?

rude man
Homework Helper
Gold Member
Per your equation, you need the current, right?

Per your equation, you need the current, right?
Yes, but the voltage is given at a later problem, so I figured why not just test it now as I'm not sure what to do. If I have the current, I would just need to plot it + find the correct reluctance to proceed.

I don't know though, it was just an idea.

rude man
Homework Helper
Gold Member
???

get the current, by hook or by crook!