One of the most important properties of a class of
materials called"superconductors" is that magnetic
fields cannot penetrate into the material. This
means they can be used to levitate magnets and
even to build magnetic levitation trains (this is
currently being done in Japan), which float 10mm
above the tracks on a magnetic field. Some
examples of superconductors that people have know
about for over 90years are Mercury, Tin, and Lead.
The only problem with these materials is that
they must be at a temperature of less than -270
degrees Celsius to work as superconductors! More
recently people are starting to discover
"high-temperature" superconductors, which work at
temperatures as high as -110 degrees Celsius
(which still sounds pretty darn cold to the
Yes- magnetic fields can't penetrate a
superconductor.They can't even pass through the
hole in a loop made of superconductor.
the basic laws of physics is that any changing
magnetic field creates an electric field, which
exerts forces on charged particles such as
electrons. Voltage is a measurement of electric
field strength, and as you know, applying voltage
to a conductor causes electrons to move.
is electricity. So, a changing magnetic field in
a conductor creates electricity in the conductor.
The effect even works when a conductor (such as a
loop of wire) encircles a magnetic field.
This is how generators work- rotating magnets
spin next to or inside loops of wire, and
electricity comes out of the wires.
also why you can fry sensitive electronic devices
by swiping a magnet past them.
explains why solar storms can cause blackouts.
Hot gas and charged particles from the Sun change
the shape of the Earth's magnetic field. This
field is weak, but the gaps between major power
lines can be hundreds of miles across. The bigger
the loop, the higher the voltage- so even a small
change in Earth's weak field can cause voltage
surges which shut down the entire grid.
to superconductors. Superconductors are materials
which conduct electricity without any loss or
dissipation- obviously a useful property! Some
common metals (such as lead) can become
superconductors, but all known superconductors
lose their superconducting ability if they're not
kept extremely cold, which is why you don't see
them used everywhere.
In a loop of
superconductor, electricity can even run around
chasing its own tail- forever. This would never
happen in an ordinary conductor because of the
problem of maintaining a voltage, but
superconductors don't need voltage to conduct.
Ohm's Law states that voltage=current*resistance,
or V=I*R. In superconductors R=0 and I cannot be
infinite, so therefore V must also be 0. If you
put a voltage on a superconductor, electricity
will always flow in a way which cancels out that
A changing magnetic field generates
voltage, so the electricity must flow in a way
which cancels the change in the magnetic field.
You know from the electromagnet that electricity
creates a magnetic field. The superconductor
automatically creates the right pattern of
electricity to generate a counter-field which
cancels any change in the magnetic field piercing
Now, if the superconductor
becomes superconducting without any magnetic field
present, no field will be able to pierce it as
long as it remains superconducting. Put the
superconductor over a magnet, and its counter-
field can even become strong enough to levitate
the superconductor by magnetic repulsion. That's
why you see those pictures of the superconductor
floating in a cloud of mist.
the superconductor is cooled below its critical
temperature while a magnetic field is present, the
superconductor will retain that field unchanged.
If the original magnet is removed, the
superconductor just becomes an electromagnet and
regenerates the field.
magnetic effects aren't foolproof, though. High
magnetic fields induce high electric currents,
which will remove the superconductor's superpowers
just as surely as high temperatures will. So, a
super-strong magnetic field will penetrate a
superconductor, but first it must make it lose its
can also transform helium into a superfluid. If
your orange juice was a superfluid, it would crawl
up the side of your glass and escape.
mineral magnetite has its own magnetic field, so
when it's in a repulsive configuration it can keep
out a magnetic field weaker than its own. This is
not a perfect shield like a superconductor,
because inside the magnetite the influence of the
opposing field can still be felt.
niobium can also become magnetized, so they can
keep out magnetic fields in the same way magnetite
Iron and niobium can also distort and
even amplify magnetic fields, but the effects
depend on the shape of the metal. You can make an
electromagnet by winding wire around a stick, but
an effective electromagnet uses a steel nail as a
magnetic amplifier. The nail not only allows the
field to pass through it, but it also makes it
stronger. However, a large steel plate seems to
block magnetic fields completely. Stick a magnet
on one side, and a steel paperclip won't stick to
the other side. The plate doesn't really block
the field, it just absorbs it and dissipates it
throughout the plate. The magnet has a small but
strong field, which the plate turns into a large
but weak field.
Any metal or other conductor
(whether nonmagnetic, such as copper, or magnetic,
such as iron) will keep out magnetic fields
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