occur when YBCO and the magnet are free and we have to admit a fundamental
difference in the two considered situations. They conclude that a phase transition
can be involved, because when T ¼ T room the superconductor does not evidence
magnetic properties, but when T ~ T NL , suddenly, magnetic properties emerge.
(S3) Students design and perform free experiments to explore the phenomenology
and to characterize the YBCO behavior. To individuate the kind of magnetic
property acquired by YBCO at T NL , a systematic exploration of its interaction
with different magnets and different materials (ferromagnetic materials in primis),
in different configurations, is carried out. The superconductor is not becoming
ferromagnetic, it is not a permanent magnet, it does not become like the mirror
image of the levitated magnet. It always shows repulsive effects close to a
magnet.
(S4) Study of the behavior of different materials interacting with a magnet to
individuate which kind of material properties are assumed by YBCO at T NL .
The levitation of pyrolytic graphite on a quadrupole of magnet is observed.
Students studied the interaction of a strong neodymium magnet with paramagnetic and diamagnetic systems suspended on a wire or on a yoke in order to make
evident even very small repulsive/attractive forces. Comparing the behavior of
diamagnetic materials with those of the YBCO at T ~ T NL it has to be classified
diamagnetic.
(S5) Intensity of the diamagnetic interaction. The strength of the interaction between
a superconductor and a magnet is several orders of magnitude greater than those
observed with ordinary diamagnetic materials, suggesting to search for a more
detailed characterization of the nature of the diamagnetism of the superconductor.
Starting from the evidence that the superconductor shows magnetic interaction
only when a magnet is close to it and that the YBCO do not interact with a
ferromagnetic object, students recognize that the interaction with a magnet does
not depend on the pole put close to the surface of the magnet, the equilibrium
position is always the same. Changing magnet, the equilibrium position changes,
but it is always the same, for the same magnet.
(S6) Discussion on the magnetic field inside to the Superconductor and search for an
explanation. Analysis of the situation: a sandwich composed by the magnet M 1 /
YBCO/ferromagnetic ring at T ¼ T room is lifted, pulling the magnet M 1. At
T ~ T NL the ferromagnetic ring is no more pulled. We have to admit that when
T ~ T NL the magnetic field inside the superconductor sample can be zero or very
little (in this condition the magnet and the iron ring do not interact when the
YBCO disk is in between). Moreover, when T NL < T < T room the magnetic field
B can exist and be different of zero inside the YBCO sample, but the magnetization of the superconductor is always adjusted to react to the external magnetic
field, tending to preserve the initial situation. In particular, if B ¼ 0 when the
superconductivity state is created, the system tends to react to an external
magnetic field creating a counter field that tends to maintain B ¼ 0 inside the
superconductor (Meissner effect).
(S7) Search for an analogy able to explain the Meissner effect. Eddy currents
produced in the electromagnetic induction have a similar behavior. A magnet is
10 Innovation of Curriculum and Frontiers of Fundamental Physics in Secondary. . .
111
difference in the two considered situations. They conclude that a phase transition
can be involved, because when T ¼ T room the superconductor does not evidence
magnetic properties, but when T ~ T NL , suddenly, magnetic properties emerge.
(S3) Students design and perform free experiments to explore the phenomenology
and to characterize the YBCO behavior. To individuate the kind of magnetic
property acquired by YBCO at T NL , a systematic exploration of its interaction
with different magnets and different materials (ferromagnetic materials in primis),
in different configurations, is carried out. The superconductor is not becoming
ferromagnetic, it is not a permanent magnet, it does not become like the mirror
image of the levitated magnet. It always shows repulsive effects close to a
magnet.
(S4) Study of the behavior of different materials interacting with a magnet to
individuate which kind of material properties are assumed by YBCO at T NL .
The levitation of pyrolytic graphite on a quadrupole of magnet is observed.
Students studied the interaction of a strong neodymium magnet with paramagnetic and diamagnetic systems suspended on a wire or on a yoke in order to make
evident even very small repulsive/attractive forces. Comparing the behavior of
diamagnetic materials with those of the YBCO at T ~ T NL it has to be classified
diamagnetic.
(S5) Intensity of the diamagnetic interaction. The strength of the interaction between
a superconductor and a magnet is several orders of magnitude greater than those
observed with ordinary diamagnetic materials, suggesting to search for a more
detailed characterization of the nature of the diamagnetism of the superconductor.
Starting from the evidence that the superconductor shows magnetic interaction
only when a magnet is close to it and that the YBCO do not interact with a
ferromagnetic object, students recognize that the interaction with a magnet does
not depend on the pole put close to the surface of the magnet, the equilibrium
position is always the same. Changing magnet, the equilibrium position changes,
but it is always the same, for the same magnet.
(S6) Discussion on the magnetic field inside to the Superconductor and search for an
explanation. Analysis of the situation: a sandwich composed by the magnet M 1 /
YBCO/ferromagnetic ring at T ¼ T room is lifted, pulling the magnet M 1. At
T ~ T NL the ferromagnetic ring is no more pulled. We have to admit that when
T ~ T NL the magnetic field inside the superconductor sample can be zero or very
little (in this condition the magnet and the iron ring do not interact when the
YBCO disk is in between). Moreover, when T NL < T < T room the magnetic field
B can exist and be different of zero inside the YBCO sample, but the magnetization of the superconductor is always adjusted to react to the external magnetic
field, tending to preserve the initial situation. In particular, if B ¼ 0 when the
superconductivity state is created, the system tends to react to an external
magnetic field creating a counter field that tends to maintain B ¼ 0 inside the
superconductor (Meissner effect).
(S7) Search for an analogy able to explain the Meissner effect. Eddy currents
produced in the electromagnetic induction have a similar behavior. A magnet is
10 Innovation of Curriculum and Frontiers of Fundamental Physics in Secondary. . .
111