# Force on a permanent magnet from an electromagnet

1. Mar 21, 2016

### Chris Fuccillo

Hi again and thank you again for the help

If I have two magnetic fields, one permanent ring magnet B2 free floating on a fixed electromagnetic coil B1 and the field are perpendicular 90 deg to each other will the free floating permanent ring magnet feel a strong magnetic torque and rotate? Ever where I read so far as long as there is a gradient or the field is at an angle greater than 0 deg there is force/torque on the ring magnet. I have not seen an example where the fields are at 90 deg/perpendicular is this special case like when the fields are at 0 deg/ parallel?

B2 = permanent magnetic

B1 = electromagnet coil

F1 = Force/magnetic torque

B2 ↑ B1→ =F1↗

Or

B2 ↓ B1→ =F1↘

If the above is true can you point me to the proper formula for calculating the force. When it comes to the magnetic fields, the distances in the calculations are in millimeters and fractions of a millimeters. I believe this leaves me stuck using formula correct? F(x)= (3μₒ/π) *m1*m1* (1/xˆ4). I think there should be a cos or tan function to it where I am at 90 deg now

2. Mar 22, 2016

### Jeff Rosenbury

Off the top of my head the magnet is marginally stable. This is like a ball balanced on the tip of a cone. It will stay there until the slightest breeze starts tipping it one way or the other. Then it falls.

Since fields are linear, two fields completely orthogonal to one another don't really interact. But tip one just a little and that's not true anymore.