Magnetostatic question: about electromagnet/permanent magnet

[Chris Fuccillo]

General Information: A coil that is wound on a magnetic core is placed in between two permanent magnets as depicted below. The coil is fixed and the magnets are affixed to a shaft and can rotate freely. Assume that there is 0 friction for the purpose of the following questions Note: arrows on magnets depict magnetic field direction.

Question 1: this question is about the core material, when exposed to an external magnetic field and no current is flowing through the coil, the magnetic domains in the material will align with the external field. When I turn on current to the Coil the field will be at an angle of 90deg, will I require more current and stronger H field beyond the normal saturation level of the core material to induce saturation in the material with the domains in the core aligning with the field produced by the coil instead of the permanent magnet field that the coil is in?

H= H field in Am

N= number turns

I= current

m = mean magnetic path length

Question 2: This question is about the torque produced and felt by both the coil and the permanent magnets. If the field between the two permanent magnets is a reasonably uniform field, can the torque be calculated using the magnetic moment of the coil in a uniform magnetic field? If it cannot be calculated this way could you point me to the proper theory and formula, as an example, would calculating pole torque be better or more accurate?

= Torque

= magnetic moment of coil

= uniform magnetic field

= Sine the angle between the fields

Question 3: This question is also about the torque. Will the torque felt by the coil and core material also be felt by the permanent magnets? Will this torque cause the permanent magnets to align with the coil and core when current is applied to the coil?

Homework Equations

The Attempt at a Solution

I am trying to double check on the current needed to saturate the coil's core material that it is wound on when its exposed to an external magnetic field I do not need help calculating the formula, I need to know if the permanent field will require me to use more current than normally required to saturate the core when its exposed to a external field. Also want to verify I can calculate torque with the above formula for torque in a uniform magnetic field. [/B]

 

[Valkarie]

Question 1: Yes, you will need to use more current and a stronger H field than the normal saturation level of the core material in order to induce saturation in the material with the domains in the core aligning with the field produced by the coil instead of the permanent magnet field that the coil is in. Question 2: Yes, you can calculate torque using the magnetic moment of the coil in a uniform magnetic field. The equation for torque is given by Torque = Magnetic Moment x Magnetic Field x Sine the angle between the fields. Question 3: Yes, the torque felt by the coil and core material will also be felt by the permanent magnets. This torque will cause the permanent magnets to align with the coil and core when current is applied to the coil.