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Why do solenoids attract ferromagnetic substances?

Physics Asked by Abu Safwan Md farhan on October 26, 2020

In this Veritasium video, Derek explains why solenoids (electromagnets) work. But I have a confusion.

He only explained the case when the solenoid (electromagnet) attracts a charged object ( that is, the cat). But he didn’t explain the case when the solenoids (electromagnets) attract uncharged ferromagnetic substances.

What would be the scenario then?

If there’s any problem in my question please inform me. Thanks!

2 Answers

Ferromagnetism means just that: it's a property of a substance being attracted by a magnet, even if uncharged. The reasons are quite fundamental and are better explained in more depth in the linked Wikipedia article.

So something like iron shavings (nickel and cobalt would work too) in some kind of liquid behave like a liquid permanent magnet that will be attracted by a magnetic field. You could check this by building a solenoid, laying it on a flat surface in a puddle of iron shavings liquid, and switching it on. Would look something like this.

Answered by John W. on October 26, 2020

A current carrying solenoid produces a magnetic field. If a ferromagnetic material is placed in that field, the atomic dipole moments are subject to a torque and brought into some degree of alignment with that field. If the material is outside the end of the solenoid (where the field is spreading), the dipoles are also subject to a net attracting force which is proportional to the gradient of the field. Permanent magnets display a similar behavior, but the dipoles may be reversed, and subject to a repelling force.

Answered by R.W. Bird on October 26, 2020

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