From CHRIS PARTON
Jim Lesurf in ‘The rise and fall of negative resistance’ (31 March)
states that some workers working with superconducting oscillatory circuits
have found that such oscillation ‘persists indefinitely without getting
any smaller’. Heaviside, in his Electromagnetic Papers, took the contrary
view, that resistanceless circuits were not necessarily loss-free, and indeed,
in oscillatory circuits, loss was to be expected.
Heaviside’s argument is highly plausible. No material is infinitely
rigid, and so it will deform periodically because of the oscillatory electrostatic
and magnetic forces in the circuit. Such deformation will be accompanied
by small temperature changes as in an ideal gas with oscillatory compression
and rarefaction. Even if the materials of the circuit are ideally elastic
there will still be losses because of the cyclic temperature changes. That
follows from the Second Law of Thermodynamics. In the superconducting circuit
envisaged, there will be excellent thermal coupling between the circuit
and the cryostat, providing a best possible route for the heat to be lost
from the circuit.
Was Heaviside wrong, or was the experiment discontinued before the difference
between zero decrement and very small decrement could be observed?
Chris Parton Glasgow
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