So, from a previous previous question, I know what plane the force from an electromagnet will affect a ferromagnetic material in. I thought that would be enough, but working through some problems using the force of a solenoid (electromagnet) given by $$F = (NI)^2\mu_0A/2g^2$$ I realized I was unsure where to get $g$ from.
I know that I should take $A$ from plane b, but what point should I take $g$ from? What point along the rod should I take the area from? The farthest away possible from the electromagnet, at the back? As close as possible, at the front? The middle of the rod, an equal distance from both ends? Should I calculate the force at all places along the rod, and average them all?
As of right now, I am assuming the force is acting on the middle of the rod (the average distance away from the electromagnet.)
Any help appreciated.
Edit: Thinking about this, I believe the real question I should be asking is "Should I be using volume and g^3 in my equation instead of area and g^2? Because the electromagnet would produce a field, acting on anything in it that is ferrous. So the force would be acting on whatever volume is "immersed" if you will, in the field?"