Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Does Aluminium Attract Magnet?

Introduction

A magnet attracts pins, coins, nails etc because these materials are ferromagnetic. They contain domains in which magnetic moments of thousands of atoms are aligned in one direction. Aluminium is a paramagnetic substance and does not contain domains. So a magnet does not attract aluminium. However when motions are involved, situation could be different.

Apparatus

An Aluminium plate, a magnet, support to hang the magnet

Procedure

Put the aluminium plate below the given support. Hang the magnet from the support and adjust the length of the thread so that the magnet is slightly above (say about 1 mm) the plate. Let it come to complete rest. Now hold the plate from one side. Make sure that the plate does not touch the magnet. Keeping the plate on the floor/platform, pull it towards one side. What did you see? Was the magnet also pulled in the same direction in which the plate was pulled?

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Discussion

If aluminium is paramagnetic then why does it exert a force on the magnet to move it? This is because when the plate is set in motion, the free electrons in aluminium experience a force due to the magnetic field of the hanging magnet. This creates an emf which results in induced currents on the surface of the plate. Theses currents produced their own magnetic field and this magnetic field exerts force on the magnet to move it in the direction of plate's movement.

When the magnet moves, relative motion between the plate and the magnet is reduced. This is consistent with Lenz's law. Induced currents are produced due to relative motion between the plate and the magnet. The currents induced on the plate oppose this reason by dragging the magnet in the direction of plate motion.