high school students face superconductivity

High School Students FaceSuperconductivity

Lorenzo Santi Research Unit in Physics Education

Department of Chemistty, Physics and EnvironmentUniversity of Udine (Italy)

[email protected]

The Physics Education Research Unit at the Udine University

Permanent StaffMarisa Michelini (full professor)

Lorenzo Santi (associate professor)

Alberto Stefanel (researcher)

PhD StudentsStefano VercellatiGiuseppe FeraEmanuele Pugliese

Associate Visiting TeachersAlessandra MossentaGiacomo Bozzo

Department of Chemistry, Physics and EnvironmentInterdepartmental Centre for Research in EducationVia delle Scienze 206, Udine, 33100, Italy

• Students’ low interest in science (PISA results PISA 2006 - Science Competencies for Tomorrow's World)

An improvement of the scientific teaching is needed

revision of the curricula enhance the scientific teaching and the teacher formation

– Re-organize classical physics introducing elements of modern physics

– Build bridges between MP and CP– Build bridges between science and technology– Adopting active teaching/learning (T/L) strategies– Promote the use of hands/minds-on

WHY SUPERCONDUCTIVY

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Introduction of SC and EM with hands/minds-on, measurements carried out by sensors, modeling, simulations, …

MOSEM and MOSEM2 Projects (Supercomet family projects: http://mosem.eu)

HOW (we are doing it)

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http://mosem.eu/

European Projects MOSEM e MOSEM2 Minds-On experimental equipment kits in Superconductivity and ElectroMagnetism for the

continuing vocational training of upper secondary school physics teachers

http://supercomet.no/

MOdelling and data acquisition for the continuing vocational training of upper secondary school physics teachers in pupil-active learning of Superconductivity and

ElectroMagnetism based on Minds-On Simple ExperiMents LIFELONG LEARNING PROGRAMME Leonardo da Vinci

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Introduction of SC and EM in upper secondary school, with hands/minds-on, integration of measurements carried out by sensors, modeling, simulations, video analysisMOSEM and MOSEM2 Projects (Supercomet family projects: http://mosem.eu)

URDF-UNIUD USB R-T & Hallon-line acquisition and modelingTeacher Training and Students LearningT/L paths from E.M. to SCActive learning (strategies IBL, Problem Solving, RTL)Tutorials based on active, inquiry based approaches and that can promote it.

HOW

In the final version of the project, Mosem2, we proposed a model of teacher training and educational experimentation based on a path on Electromagnetism and superconductivity, using more than 100 simple and 8 high tech experimental apparatuses.

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All this is inserted in a path of work in classroom, with computer modeling activies and measurement with online sensor data acquisition or demonstrative experiments.

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The educational tools LOW TECH KITMagnetic interactions, E.M. induction, Eddy currents

HIGH TECH KIT

Fig. 4.1.2A Experimental set-up components.

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The educational tools

Critical Temperature of YBCO

• YBCO. • Temperature Sensor

• Heater

HIGH TECH KIT

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The educational toolsTemperature dependence of resistance

HIGH TECH KIT

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Hall Effect

HIGH TECH KIT

Persistent currents Levitation

pinning

The MAGLEV trainPara-Ferromagnetic

transistion (gandolynium)


The educational path

Magnetic properties of superconductor- Interaction between magnets (exploration and discussion by

means of field lines rappresentation)- Meissner effect- E.M. induction and eddy currents- The pinning effectResistivity vs temperature- Temperature dependence of resistivity for metals and

semiconductors- The Hall effect- Critical temperature for a superconductor

Research experimentations: (since 2006)

Laboratory activities in school (national plan for scientific orientation)Summer schools for upper secondary school studentsPreservice and in service teacher training experimentations

In the last two years:

8 contexts (UD-PN-CS-BA-KR -SI: 295 students )

Explorative activities (informal learning):4 contexts (UD-PN-Frascati- 685 students)

• Which topics in superconductivity can be introduced by means of the phenomenology?

• How students face the main conceptual knots?

A full example:Exploring the phenomenology of the Meissner effect

Aim : to understand correctly the effect in the framework of the magnetic interaction between objects.

Tools needed: A disc of YBCO (YBa2Cu3O7), Tc ~ 90

A bath of LNA (few) magnet(A compass)(A B field probe)

Preliminar exploration with compasses or magnetsThe YBCO, at room temperature, does not interact with any magnet

When the YBCO is brought to thermal equilibrium in a bath of LN(77K) …… it interacts with magnets

levitation

At lower temperature

• Have the properties of the magnet changed? • Have the properties of the YBCO disk changed?

How?• How can we interpret the changes?

Questions

• Are the properties of the magnet changed? Wherever the magnet is at Te or at TNL , its interactions

with other objects (not YBCO) are qualitatively (and essentially quantitatively also) unchanged.

The B field measured around a magnet with a B probe, has the same intensity (and direction)

• Are the properties of the YBCO disk changed? – Before the YBCO disk doesn’t interact with the

magnet– Then the YBCO interact strongly with the magnet

Yes, (Only) the magnetic property of the YBCO are changed

• In which way? Hypotesis

• The YBCO becomes a ferromagnetic object?If the magnet is reversed (180° rotation), levitation occurs in the same way: it is always a repulsive effect! When a magnet interact with a ferromagnetic object

there is an attractive effect

NS

SN

No: the YBCO disk does not become ferromagnetic

• The YBCO becomes a magnet and it interacts with another magnet as they are facing with the same polarity?

MagneticSuspention

Magnetic levitation of a magnet on a SC

MAGNET

SUPERCONDUCTORMAGNET

MAGNETconstrained

free

No: the YBCO disk does not become a magnet

! Two magnets repeal each other only when they are constrained to face with the same polarity rotation and attraction

The YBCO disk at T=TNL, evidence the property to repeal the magnet in any case ?

Yes, the YBCO evidence the property to repeal in any case a magnet

–If we move gentle the magnet, it oscillate around a local equilibrium position –If we use a magnetic cube it will rotate till its magnetic axe becomes approximately horizontal–-When we put a magnet close to the side of the YBCO disk a repulsive effect it occurs in any case

• If the magnet is reversed, levitation occurs in the same way: in any case a repulsive effect will happen.

• The YBCO disk at T= TNL “acts” magnetically without the magnet close to it? For instance, can we expect an interaction between an iron clip and the YBCO disc?

The YBCO does not “act magnetically” without a magnet close to it

-An experimental test will be in any case dramatically negative: nothing happens in any case

What kind of magnetic property we are analyzing?

- Exploration of the interaction of a magnet with different types of materials (aluminum, copper, water, wood, graphite) by hanging these and see if they are attracted, repulsed or not affected by the magnet.

Diamagnetic materials: they show “magnetic properties” (repulsive) only in presence of the magnet Pyrolitic graphite levitates too The YBCO disk at low temperature becomes diamagnetic

The diamagnetic phenomena are usually weak.In the case of the SC the diamagnetic effects are very intense.To understand, we have to “see” what happens inside the YBCO.

-Does the external field of the magnet penetrate the YBCO?We can test that.

If you make a sandwich magnet – YBCO – iron slab

- At T=Te you can lift it by pulling the magnet We know that the magnet has no effect on YBCO at this temperature, so there is an action of the magnet on the ironThe field of the magnet “arrives” on the iron passing through the YBCO

A magnetic field can exists in YBCO at room temperature

- At T=TNL this effect usually disappears and you can’t lift YBCO and iron (Note: this is not completly true if there is some pinning effect). The field of the magnet can’t “arrive” on the iron and we can conclude is really small or negligibile through the UBCO

The magnetic field inside a YBCO at LN temperatures is negligibile.

A. Stefanel, URDF-UNIUD Lab SupCond-Pigelleto 29

Is the the field zero inside the YBCO or just very weak?-The same magnet leaved over the YBCO at T=TNL levitate at the same height-If we change the magnet the height of levitation changes, but is the same for each magnet-Measurements of B just out side the YBCO

For a defined range of the external B field the YBCO reacts to it The current increase as the magnet goes closer to the YBCO

A students’ outcome example

• Summer School Pigelleto 8-10 sept 2010 (PLS-Università di Siena IDIFO3/MOSEM2)

• Didactic Lab on SC - 3,5 h (MOSEM2 experiment ed poroposals).

• 40 students (17 – 18 years old)

4 IBL Worksheets for the learning path.

Worksheet 1 – Interaction between magnets (discussion using field lines representations)Worksheet 2 – Meissner effect

The ideas of students

SC 2 – Interaction between magnetic dipoles

C. Draw the field lines, after the transition. Explain the picture

4/40

10/40

4/40

4/40

22/40 the field lines do not penetrate the Ybco if T<TNL

Tamb

TNL

Tamb

TNL

Tamb

TNL

Tamb

TNL

15/40 SC produces a field (modell magnet/magnet)3/40 the lines penetrate SC at T>TNL

3/40 7/40 8/40

Tamb

TNL

Tamb

TNL

Tamb

TNL

C. Draw the field lines, after the transition. Explain the picture




12/40 «the properties of the YBCO have changed»«the decrease in the temperature produced a change in the

behaviour of the YBCO»

14/40 «The disc of YBCO changes its properties. It repels the magnetic field»

5/40 «The YBCO disc is magnetized»

3/40 Re-arrangement of the atoms

6/40 NR

B3.1 Have the properties of the magnet canged?B3.2 Have the properties of the YBCO changed? B3.3. What are the properties changed and in which way?


-Use of the line field representation to take into account : - The repulsion (37/40, but one third following the magnet magnet

repulsion scheme)- Peculiarity of YBCO (B=0) (25/40 in the rappresentation, 27/40 nin the

explanations)- Change of magnetic properties

-Features included in the explanations:- Levitation (without constraints) (2/33/3)- Null field (2/3)- Process that happens at the decreasing of T and it changes the YBCO

properties (40) below a threshold temperature (1/2)

Summary of the results for the L path on Meissner effect

E.M. Induction and eddy currents

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NS

S1

NS

S1(B)<MAX

S0(B) MAX

2

0

1

S2(B)<MAX

S2

S1

Bo

Conceptual tools: Field lines (operative definition)The flux of B ((B))The FNL law

NS

S1

NS

2

0

1

S2

S1

Bo

S2(B)/ t = (S2(t) - S2(0))/ t= (S2(B) - MAX(B))/ t <0

S1(B)/ t = =(S1(t) - S1(0))/ t= (MAX(B) - S1(B))/t >0


NS

S1

NS

2

0

1

S2

S1

Bo

Iind DL -F

F

-F = Iind (LB)

F = -(-F)


Lifting (braking) effect

Corrispondence between the “braking” of the magnet in presence of a conductor

and the levitation, if the conductor is “perfect” (R=0) and the currents initially induced by the magnet never stop.

Superconductor : a system with B=0 and R=0!

Meissner effect vs pinning

Train a la Meissner Train “pinned”

• Activity experimented in three summer schools for selected students of all Italy 17-19 aged (Univ. Udine)

• Udine 2007 (50 students)• Udine 2009 (40 Students)• Udine 2011 (40 students)

Temperature dependence of resistivity

Temperature dependence of resistivity

Lab SupCond-Pigelleto 44

Free cooling in LN

Heating step by step

20% of answers: only the final temperature of the transition is recognized

80% of answers: The full transition interval is recognized

Conclusions

Activities highly motivating that lead to significant partecipation (and learning)

Even in front of a complex phenomenology (see for example the puzzling difference between the Meissner effect and the pinning), the students are able to acquire the conceptual tools to descrive and analyze the phenomena involved and to develope models that take into account the relevant aspect of the superconductivity.

Strong integration with “traditional” topics in E.M.

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LOW TECH KITThe educational tools

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What happens if the magnet is before putted over the YBCO disc and then dipped into the LN?

- The magnet levitates The YBCO disc repeals in any case the magnet

A. Stefanel, URDF-UNIUD Lab SupCond-Pigelleto 53

high school students face superconductivity

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