At full contact, the attractive force between a raw magnet and an iron plate is the same as the attractive force between two raw magnets. However, with increasing distance, the attraction diminishes faster than the attraction between two raw magnets (see graph)

I am confused by this:

  1. Consider two identical Electromagnets touching each other in one case and a single electromagnet touching an iron plate in second case. Won't the attraction be more in the first case as both magnets are exerting a pull on each other where as in second case the magnet is pulling on a passive iron plate (which has temporarily induced magnetism)?

  2. For two cylindrical electromagnets with poles at distance $x$ repelling each other (they are relatively close by i.e. $10*R > x$ where $R$=radius of pole) how does the force exerted on each electromagnet change with increase in current ($I$)? Can someone help with this formula?


1 Answer 1


For #1: Iron is not magnetically passive. Small portions of the iron will have magnetic fields, but they are not aligned. They do not work together on the outside world. When a magnet (electric or otherwise) touches a piece of iron, the magnetized zones in the iron become more aligned as the iron atoms become more organized. The stronger the external magnetic field, the more magnetized the iron becomes. When the external magnetic field is removed, small scale effects such as temperature make the iron less organized, but the piece of iron will maintain some of the magnetization. The external magnetic field causes the iron to become a strong magnet by aligning many small magnets. These many small magnets now work together to pull on the electromagnet.

  • $\begingroup$ Thanks but I am aware of this part. 'passive' in the sense it does not have its own net macroscopic magnetic field. So an induced magnet pulling on a magnet/electromagnet is as strong as two magnets/electromagnets? This is what i am struggling with! Can you provide an academic source for the same? $\endgroup$
    – J.Doe
    Commented Dec 5, 2022 at 19:57

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