As The Meissner effect is an expulsion of a magnetic field
from a superconductor during its transition to the superconducting state.
The
German physicists Walther Meissner and Robert Ochsenfeld discovered the
phenomenon in 1933 by measuring the magnetic field distribution outside
superconducting tin and lead samples. The samples, in the presence of an
applied magnetic field, were cooled below their superconducting transition
temperature. Below the transition temperature the samples cancelled nearly all
interior magnetic fields. They detected this effect only indirectly; because
the magnetic flux is conserved by a superconductor, when the interior field
decreased, the exterior field increased. The experiment demonstrated for the
first time that superconductors were more than just perfect conductors and
provided a uniquely defining property of the superconducting state.
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The Casimir effect is a small attractive force that acts
between two close parallel uncharged conducting plates.
It is due to quantum
vacuum fluctuations of the electromagnetic field. The effect was predicted by
the Dutch physicist Hendrick Casimir in 1948. According to the quantum theory,
the vacuum contains virtual particles which are in a continuous state of
fluctuation. Casimir realised that between two plates, only those virtual
photons whose wavelengths fit a whole number of times into the gap should be
counted when calculating the vacuum energy. The energy density decreases as the
plates are moved closer, which implies that there is a small force drawing them
together. Plasma actuators are a type of actuator currently being developed for
aerodynamic flow control. Plasma actuators impart force in a similar way to
ionocraft.
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