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Superconductivity an extremely cool but expected
phenomena used for:
Levitating objects, It's used for MRI Scanners,
and it might just one day revolutionize completely
how we transport energy.
In this video i will tell you the Physics
behind it and a little bit of the history
as well.
Superconductivity was discovered in 1911 By
Heike Kamerlingh Onnes.
It was just made possible to liquefy Helium
which produces extremely cold temperatures.
Here, on this temperature scale we have Celsius.
And at zero, off course, water freezes. and
at 100 degrees celsius water boils.
At negative 273 we have the absolute zero,
and a little warmer is the liquid helium,
but it still extremely cold.
To put things into perspective here is liquid
nitrogen.
It's negative 273 degrees celcius.
Let's switch units to kelvin off we just set
the absolute zero at the zero point on this
scale here.
So you can see the temperature.
Now for my American friends here is the same
scale but with Fahrenheit instead just so
you can get a feeling of the temperatures.
Know we can reach temperatures down to 3 Kelvin!
We can use that to take a look at circuits.
So here we have a battery and we have a cable
connecting it.
That will off course induce a flow of electrons.
If we zoom in on the cable, off course the
cable is a conductor so we will see the metallic
lattice and we will see that the electrons
are loosely bound to the nucleus.
Such that they will move easily when feel
a potential.
Now compare that to an insulator: Their electrons
are strongly bound to the nucleus so it won't
conduct.
Unless we give it enough energy.
Just as you know form thunder.
You wouldn't say atmospheric air is a really
good conductor but there is just too much
energy in the system.
So the air will conduct indeed.
Anyways if we got back and take a look at
the cable again.
Off course this was a bit an idealized model
because we have temperature in the system.
This mean that we will random movements.
The random movement will cause particles to
collide and loose energy into thermal energy.
So a higher temperature will cause more energy
loss and will cause off course bigger resistance
in the cable.
Let's graph that on the X axis we have temperature
on the y axis we have resistance and as temperature
increase so does the resistance.
Actually at the time it was not known what
will happen if we drop the temperature further
- would the resistance drop to zero, as the
temperature reaches zero? or would it perhaps
reach a constant resistance?
Or maybe even too could would cause even more
resistance?
That wasn't known at the time but now with
the extremely cold liquid helium we can just
take our system, take a look at a fraction
of the cable, apply extremely cold liquid
helium to it, and measure what happens to
the resistance in that area.
Are you ready?
Because for some materials this happened:
after being cooled down under some specific
temperature called the critical temperature
there is absolutely no resistance at all.
Why?
why.
WHY?
WHYYYY?
WHYYYYYH?
Okay we will get to the Why in a second, I
just wan't to point out that we know there
is NO resistance at all in the conductor,
you know there might just be an extremely
small resistance, but there is none.
We know this because we can create a ring
out of superconductive material, let a current
run, leave the system for years and come back
later.
THis has been done, but there is no measurable
loss of the intensity of the current.
Also i wan't to point out that superconductivity
is not really a rare phenomena.
Here in this periodic table i marked all the
superdonctivie materials.
You can see it's actually quite common to
be superdontive.
Okay so know we will get to the why there
is no resistance.
Let's come back to our conductor and observe
just one electron and assume the conductor
has been cooled down by helium so the thermal
vibrations are negligible.
As the electron is being pulled to the positive
side of the battery, it flies in between atoms
of the lattice.
These atoms are positively charged because
they have lost their electron to the conduction.
This means that the electron will cause a
slight attraction of the atom.
Since it's negatively charged and the atom
are positively charged.
If you have positive atoms clump together
in a local disturbance, they are a bit more
positive.
Now, a new electron flying in will be attracted
to this local disturbance.
Because it is slightly more positively charged.
You would probably expect, since like charges
repel these two negative electrons should
repel each other.
But they don't because in reality many more
atoms in the lattice are actually a part of
this disturbance.
And the attraction happens over hundred to
thousand of atoms.
The attraction causes these to electron to
go together and bind to what is called cooper
pair.
But this bound is extremely weak, and even
thermal vibrations would break it.
That's why we needed the liquid helium.
When two electrons go into a cooper pair something
interesting happens.
Protons neutrons and electrons are usually
what is called a fermina particle.
There is another type of particle called the
boson.
A photon is a boson.
I am not going into details about this, but
being a fermion like the electron means that
no two particles can be in the same state.
That's why we see atoms like this.
We have fermions, electron orbiting the nucleus
if they were boson instead, they could all
go into the same state.
So they would all clump into the ground state
and no chemical reaction could occur.
But bosons can be in the same state.
And that's important for superconductivity.
Because when two electrons go into a cooper
pair, they are still fermions but they act
together as a boson.
That means all the cooper pairs clump into
the lowest energy level they will all be in
the same state, because they are boson now,
and not fermions anymore.
Know they can behave as one big group of particles
in the same state.
Because the cooper pairs are bounded over
a big distance more cooper pairs become overlapped.
This new big overlap becomes entangled and
now behaves as a large network of interactions.
This network of interactions will be attracted
to the batteries pole and therefore conduct.
The collective behaviour of all the electrons
in the network and in the solid prevents any
further collision with the lattice: if ti
were to collide with an atom the network can
just recombine into new cooper pairs.
To have resistance the whole network would
have to collide with the lattice, and that's
just too uncertain to happen.
So there is none.
Another way to think of it is the current
has to be resistance less because you can't
take any energy from a system that's already
in its ground state.
which these bosons are.
So superconductivity is just a strange quantum
dance of copper pairs, electrons and vibration
in the lattice.
There is much more to a superconductor than
just zero resistance.
Let's first take a look at the magnetic properties.
If we put a normal magnet here the magnetic
fields are often drawn like this.
They represent the direction and the strength
of the magnetic field.
So if we have other magnets they would certainly
be affected by it and would align to this
field.
if we have normal matter like this little
cylinder here, and put it next to a magnet
the magnetic field would just pass right through
it like nothing happened.
But if we replace the cylinder with a superconducting
cylinder the cylinder would just repel the
magnetic field.
It will not have any magnetic field inside
of it.
This happens because the electrons inside
the superconductor create small vertices that
repels the magnetic field.
Kind of like really really small electron
coils.
Now we are actually ready to create really
fast levitating magnetic superconductor trains.
Because if we have a magnet up here you can
see the magnetic fields.
And we have a superconductor down below, the
superconductor will not have the magnetic
fields inside of it so this will not happen.
The superconductor repels the magnetic fields
and therefore the magnets levitates.
There is two types of superconductors: Type
1 and type 2.
What we talked about until now is all governed
by type 1 superconductor.
Sadly we don't know how a type 2 superconductor
works.
But that's really a shame because type 2 superconductors
works on higher temperatures and really interested
in knowing that because if we knew we could
put up a lot of solar cells on africa transport
all the energy up the country that needs extra
energy.
Without any loss of intensity and therefore
solve the energy crisis.
Any day perhaps.
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