Physics Photo of the Week

FEBRUARY 17, 2012

Levitating Magnet - Photos by Liz Miller.  Discussion by Hannah Fearing

The phenomenon seen in these images is known as the Meissner Effect.  Here, a magnet levitates just above a disk of special material called a superconductor.  It is called a superconductor because it conducts electricity very well at low temperatures.  It has absolutely zero resistivity meaning the electricity can flow through it forever without dissipating any energy.  Besides conducting electricity perfectly, superconducting materials like the one shown (YBa2Cu3O7) repel magnetic fields at low temperature.  Usually, the magnetic field surrounding a magnet passes through the material, meaning the magnet would sit on the surface of the material.  However, when the material begins superconducting at low temperature, the magnetic field is repelled, and the magnet levitates. 

In the picture, liquid nitrogen is used to cool the YBa2Cu3O7 to its transition temperature (the temperature at which it begins behaving as a superconductor), and the magnet floats.  The magnet is stable, hovering just above the disk instead of flying off to one side or the other, because the material is a ceramic.  Ceramic materials are made up of many individual granules.  Each individual grain making up the ceramic repels the magnetic field.  The spaces between the grains sort of trap the magnetic field, keeping the magnet stable.

Visit the PPOW for last year (Feb 18, 2011) and see a video of the onset of the magnet's levitation as the YBa2Cu3O7 is cooled to below the transition temperature.


Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.

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