Calculating Magnetic Flux in Spool Coil with Air Gap - Formula and Example

[Mutaja]

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.

Homework Equations

The Attempt at a Solution

Using the equation: phi = I * N / R_m, I still miss I, and I have no idea how to compute it. R_m 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.

 

[rude man]

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!

 

[Mutaja]

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]

Per your equation, you need the current, right?

 

[Mutaja]

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]

?

get the current, by hook or by crook!