The Naked Scientists
  • Login
  • Register
  • Podcasts
      • The Naked Scientists
      • eLife
      • Naked Genetics
      • Naked Astronomy
      • In short
      • Naked Neuroscience
      • Ask! The Naked Scientists
      • Question of the Week
      • Archive
      • Video
      • SUBSCRIBE to our Podcasts
  • Articles
      • Science News
      • Features
      • Interviews
      • Answers to Science Questions
  • Get Naked
      • Donate
      • Do an Experiment
      • Science Forum
      • Ask a Question
  • About
      • Meet the team
      • Our Sponsors
      • Site Map
      • Contact us

User menu

  • Login
  • Register
  • Home
  • Help
  • Search
  • Tags
  • Member Map
  • Recent Topics
  • Login
  • Register
  1. Naked Science Forum
  2. Non Life Sciences
  3. Physics, Astronomy & Cosmology
  4. Why does an electromagnet attract steel but repel aluminium?
« previous next »
  • Print
Pages: [1]   Go Down

Why does an electromagnet attract steel but repel aluminium?

  • 2 Replies
  • 22820 Views
  • 0 Tags

0 Members and 1 Guest are viewing this topic.

Offline chris (OP)

  • Naked Science Forum King!
  • ******
  • 7947
  • Activity:
    2.5%
  • Thanked: 273 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Why does an electromagnet attract steel but repel aluminium?
« on: 06/08/2010 09:01:46 »
This interesting question surfaced on the radio today (thanks Albert!) and I'd be interested to hear how people here would explain it...

Chris
Logged
I never forget a face, but in your case I'll make an exception - Groucho Marx - https://www.thenakedscientists.com/
 



Offline Soul Surfer

  • Naked Science Forum King!
  • ******
  • 3384
  • Activity:
    0%
  • Thanked: 6 times
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Why does an electromagnet attract steel but repel aluminium?
« Reply #1 on: 06/08/2010 10:04:49 »
Presumably your electromagnet was energised using an alternating current which means that the magnetic field is changing constantly and reversing in direction cyclically.

Steel is magnetic and will be polarised by the field and produce an amplified magnetic attraction. This will be attractive either way.  Just like iron nails are attracted to either pole of a permanent magnet.

Aluminium is non magnetic and this does not happen.  However it is a good conductor of electricity and the changing magnetic field will induce "eddy currents" in a block of conducting material.  the net effect of these eddy currents is to produce a weak magnetic field that opposes the field of the electromagnet so the aluminium is repelled by the AC electromagnet.

You can see this effect happening with a permanent magnet and a superconductor which generates enough opposing magnetic field as the superconductor approaches the magnet to suspend it over the magnet.  In normal non superconductors the electrical resistance causes the eddy currents to die away quite quickly.

Why then is the steel not repelled because it too is a conductor of electricity?  Firstly steel is a much worse conductor of electricity than aluminium so the eddy currents are smaller and die away quicker and secondly the ferromagnetic induction polarising the electrons in the steel produces a much stronger field.

Logged
Learn, create, test and tell
evolution rules in all things
God says so!
 

Offline RD

  • Naked Science Forum GOD!
  • *******
  • 9094
  • Activity:
    1%
  • Thanked: 151 times
    • View Profile
Why does an electromagnet attract steel but repel aluminium?
« Reply #2 on: 06/08/2010 10:48:13 »
Aluminium isn’t diamagnetic (it's paramagnetic) but can appear to behave like a diamagnet, i.e. repel a magnet, if moved towards one,  but this is due to induced currents (lenz law).

The same repulsive force between aluminium and a magnet also occurs if the magnet is an electromagnet powered by an alternating current, (alternating field), e.g.

[also
start to 1:15]
« Last Edit: 06/08/2010 11:02:35 by RD »
Logged
 



  • Print
Pages: [1]   Go Up
« previous next »
Tags:
 

Similar topics (5)

Does heat repel heat?

Started by guest39538Board Physics, Astronomy & Cosmology

Replies: 25
Views: 16718
Last post 23/04/2015 19:46:43
by alancalverd
What is "Stronger than Steel"?

Started by CliffordKBoard Technology

Replies: 11
Views: 30785
Last post 22/05/2017 18:00:16
by alancalverd
Could matter and anti-matter attract?

Started by thedocBoard Physics, Astronomy & Cosmology

Replies: 6
Views: 4805
Last post 23/02/2016 23:45:26
by Ethos_
Box - matter and anti-matter attract?

Started by guest39538Board That CAN'T be true!

Replies: 8
Views: 4087
Last post 01/02/2019 11:39:59
by QuantumGravity
How fast does a magnet attract ?..and other magnet questions !

Started by neilepBoard General Science

Replies: 6
Views: 15120
Last post 08/03/2007 15:48:56
by science_guy
There was an error while thanking
Thanking...
  • SMF 2.0.15 | SMF © 2017, Simple Machines
    Privacy Policy
    SMFAds for Free Forums
  • Naked Science Forum ©

Page created in 0.148 seconds with 40 queries.

  • Podcasts
  • Articles
  • Get Naked
  • About
  • Contact us
  • Advertise
  • Privacy Policy
  • Subscribe to newsletter
  • We love feedback

Follow us

cambridge_logo_footer.png

©The Naked Scientists® 2000–2017 | The Naked Scientists® and Naked Science® are registered trademarks created by Dr Chris Smith. Information presented on this website is the opinion of the individual contributors and does not reflect the general views of the administrators, editors, moderators, sponsors, Cambridge University or the public at large.