Magnetic moment of solenoid

**Jake110** · Nov12-09, 01:15 PM

Could someone show me how to calculate the magnetic moment of a solenoid, it's an air gap solenoid, 12V power supply, 1200 turns, 6cm long, the current works out to around 5-7 A and uses 1mm wire (18 AWG or 19 SWG). the flux density works out at about 3 Teslas.

If what I'm using it for effects how you calculate it, I'm using it to work out the intensity of the magnetic field which I can then use to calculate the force applied to an object near the solenoid.

**Bob S** · Nov12-09, 10:51 PM

Hi jake-
In the attached thumbnail, in fig B, reverse the location of the gap so it is inside the coil and as short as possible. A shorter gap is better. Also, the cross-sectional area of the permeable material outside the coil should be at least twice the cross-sectional area of the coil itself.
Bob S

**Jake110** · Nov13-09, 03:33 AM

so I'm i getting this right, its the same if the gap is vertical through the coil from the top to the bottom? so then G would be the horizontal distance of the gap?

**Bob S** · Nov13-09, 12:54 PM

Originally Posted by Jake110

so I'm i getting this right, its the same if the gap is vertical through the coil from the top to the bottom? so then G would be the horizontal distance of the gap?

Hi Jake-
The size of the gap G is always the length measured along the field lines, and it should be small relative to the total length measured around the magnetic loop. The field in the gap is strongest if it is inside the solenoid coil.

B = u₀NI/G Tesla in the gap.

Bob S