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.
All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion. These photos and discussions may be used for private individual use or educational use. Any commercial use without written permission of the photoprovider is forbidden.
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