While looking at reviews for Caver A. Mead's book, I read a review that said he
made a mistake including voltage in a calculation for superconductors.
Now I think that there must be voltage of a type in superconductors, there are
2 types of voltage.
One is the voltage drop across a conductor. This is similar to the voltage on a
charged capacitor.
But there are other type is kinetic voltage, this is where a charge is moving
at a given velocity as it used in particle accelerators.
>Voltage of this type can be compared to (or come from) inertia, and if
>electrons are moving then there will be some persistence even if impedance is
>removed since electrons still have mass.<
There is no need to apply a voltage across the leads of a superconducting loop
for current to flow. Any current present will continue indefinitely. And, if
you do apply a voltage, the current will ramp up as long as the voltage is
applied. The ramp rate is established by the voltage you apply and the
inductance of the loop.
>If a superconducting ring that carried a current was suddenly opened, the
>electrons are still moving and must compress slightly as they come to a stop
>leaving the ends momentarily charged to some degree.<
All of the energy stored within the magnetic field must be either converted
into heat by arcing across the open circuit and heating the air, or by charging
the effective capacitance formed by the open leads. The energy given to the
capacitor will be returned to the loop inductance when the current reverses and
this process can ring indefinitely as long as the loss is zero.
>Additionally imagine a superconductive loop in an alternating EM field, there
>is a voltage induced by the changing magnetic field (or relativistically
>distorted electric field) and this does not lead to a voltage drop, but there
>is still a voltage, if this loop was opened and a normal circuit inserted you
>would indeed see a voltage.<
There is a voltage drop in this case due to the AC current induced within the
loop flowing through the loop inductance. It does not lead to heat because the
voltage and current are at right angles to each other.
>Indeed even if we use a resistive wire in such a loop, no voltage drop is
>noted, and yet there is still a voltage present to overcome the resistance,
>and the resistance is still impeding the flow of electrons. But would it be
>correct to say that this is happening with no voltage, even though none can be
>read by any instrument?<
Perhaps I do not understand what you are saying here as I would expect to see a
voltage drop measured across the ends of any resistor carrying current. The
resistive wire case would show a drop that increases the further along the
resistive line you go. Of course, you must choose some point as the reference
of zero volts.
]John
Dave
