CN102723025A - Teaching instrument for demonstrating superconducting characteristic - Google Patents

Abstract

The invention relates to a teaching instrument for demonstrating a superconducting characteristic. The teaching instrument comprises a superconducting ring, a magnetic rod, a magnetic block, a Dewar, a stainless steel ring, an aluminum ring, a copper ring and a magnetic block cushion, wherein the superconducting ring is manufactured by a high-temperature superconducting closed coil. The magnitude and direction of impedance of generated induced current and an induced current magnetic field to an original magnetic field when the magnetic flux of a closed loop consisting of three common metal materials and a superconducting wire is changed are compared to understand a Lenz's law, the zero-resistance characteristic of a superconducting material and peculiar characteristics of different metal materials. The teaching instrument also can be used for finishing the demonstration of a magnetic levitation experiment by using the high-temperature superconducting ring and the magnetic block.

Description

A kind of instruments used for education of the superconducting characteristic of demonstrating

Technical field

The present invention relates to a kind of instruments used for education, relate in particular to a kind of experimental apparatus that can demonstrate Lenz law and super-conductive magnetic suspension phenomenon.

Background technology

Superconducting phenomenon is meant that certain material is being lower than a certain temperature when (being called superconducting transition temperature Tc), the phenomenon of resistance vanishing.First superconductor was found in 1911.It is called as cryogenic superconductor.Only be cooled to subzero 2690C (4K) and just can demonstrate superconductivity.Because it is extremely expensive to reach the cost of low like this temperature, so the practical application of this type I superconductors I is limited.1986, the discovery of high-temperature superconductor (HTSC) made a critical breakthrough in the superconduction field, to have occurred.Because cooling condition and cost are and are cheap, so HTSC has actual application value.

Superconductor not only has excellent electric conductivity, and also has special diamagnetism.At present, the Bi-2223/Ag superconducting wire Tc that generally uses is higher than the liquid nitrogen boiling point, belongs to high temperature superconducting materia.Resistivity and copper conductor the resistivity when temperature be 20 ℃ of this lead under superconducting state differs 1.75 ten thousand times.Theoretically, keeping under the constant situation of external condition, the electric current in the superconductor can be decayed hardly.

Britain physicist faraday in 1831 finds that the magnetic field of electromagnetic induction phenomenon-variation can produce induced current in conductor circuit.The direction that Russian physicist Lenz in 1934 proposes induced current always hinders the rule of magnetic flux change, i.e. Lenz law.The lecture experiment that a checking Lenz law is arranged in traditional for many years physics experiments of high school textbook; Demonstrate through single turn aluminium ring magnetic flux change and since the magnetic flux change of single turn aluminium ring a little less than, the induction electromotive force of generation is smaller; Induction current is smaller; Therefore faradic magnetic field is not strong, the magnetic field force between former magnetic field and the induction current a little less than, thereby experiment effect is not clearly.

Under unusual low temperature environment, the superconductor copper conductor transmission more long-pending than same cross-sectional can more electric current.Use the stronger magnetic field of coil generation of superconductor coiling can produce magnetic levitation.This phenomenon makes maglev become possibility.Because in suspension and the friction force between the air very little, like this train at the volley only the very little energy of needs promote.

Summary of the invention

The object of the present invention is to provide a kind of experiment effect obvious, and both can verify Lenz law, can demonstrate the experimental apparatus of super-conductive magnetic suspension again.

This experimental apparatus is a kind of instruments used for education of the superconducting characteristic of demonstrating, and comprises superconducting ring, bar magnet, magnetic patch, Dewar, stainless steel ring, aluminium ring, copper ring, Dewar and magnetic patch pad.Superconducting ring in this experimental apparatus is processed with the high-temperature superconductor closing coil; And this closing coil is turned to by hts tape, and described superconducting wire can be any in the second generation hts tape of YBCO series of Bi-2223 superconducting wire or overlay film.The connection of said closing coil can be to adopt superconduction to connect or welding formation closed-loop path, and connection length is 1～15cm.Described closing coil can be the two cakes of coiled, single cake, a plurality of pairs of cakes or solenoidal form, and this closing coil can enclose by coiled more, also can the coiled individual pen, and the line length of using of coil is 5-50m.The curing when making of this closing coil is to use epoxy resin or epoxy resin doped aluminium powder to come solidifying and setting.Described Dewar is processed by thermal insulation material preferably, can be by vacuumizing in the middle of the nonmagnetic substances such as aluminium alloy or stainless steel and process, also can being processed by metal material parcel thermal insulation material.

When demonstration Lenz law confirmatory experiment; Mainly be when relatively the magnetic flux of three kinds of common metal materials and closed-loop path that superconducting line constitutes changes, zero resistance property and the consequent unusual characteristic that is different from metal material that Lenz law and superconductor are familiar with to the size and the direction thereof of former magnetic field inhibition power in the induced current of generation and induced current magnetic field.Be to adopt Bi-2333 series high temperature superconducting materia to process superconducting ring among the present invention; With metal bar and permanent magnet as bar magnet; Bar magnet is inserted in stainless steel ring, aluminium ring, copper ring and the superconducting ring with identical speed; Bar magnet produces the resistances of different sizes in four kinds of materials, the experimenter can experience a certain ad-hoc location at different rings, and the suffered resistance of bar magnet is obviously different.Bar magnet in these instruments used for education is made up of permanent magnet and metal bar; It is the rod processed of the ferromagnetic material of 10-20cm or the end of bar that permanent magnet is adsorbed on length; Permanent magnet can be cylindrical, rectangle or annulus; The length of permanent magnet is 1～5cm, and permanent magnet can be alloy permanent magnetic material or ferrite permanent-magnet materials, preferred neodymium iron boron magnetic body and ferrimagnet.Closing coil can use the textile that is prone to the absorption liquid nitrogen to coat, and can be cotton, burlap, knitting wool, silk or fibers material, adsorbs a certain amount of liquid nitrogen with this and makes coil in the certain hour that breaks away from liquid nitrogen environment, keep superconducting state.

The key property Meissner effect of superconductor-found in 1933 by W.Meissner.When superconductor is cooled to its critical temperature when following under low-intensity magnetic field, superconductor gets into superconducting state---and its resistance is zero.The magnetic line of force is discharged from superconductor is inner, thereby superconductor shows perfect diamagnetism, and this characteristic just is Meissner effect.Pure Meissner effect only just can be observed under low-intensity magnetic field.If what use is that high-temperature superconductor (belonging to a type I superconductors I that can pass through high-intensity magnetic field) situation is complicated more.Under high-intensity magnetic field, only some is discharged from the magnetic line of force, and a part of magnetic flux passes superconductor, uses liquid nitrogen as cooling medium superconductor to be cooled under the critical temperature, can demonstrate Meissner effect at an easy rate.Instruments used for education of the present invention utilize liquid nitrogen as cooling medium superconductor to be cooled under the critical temperature, can easily demonstrate the phenomenon that the magnetic line of force is discharged from, checking Lenz law when experiment can be clearly the characteristic Meissner effect of checking superconductor.

The super-conductive magnetic suspension phenomenon is that cooling takes place under the superconductor outside magnetic field.Put into magnetic patch earlier and cool off superconducting ring again, it is cold that this type of cooling is called the field.Do not having to cool off superconducting ring under the external magnetic field situation, it is cold that this type of cooling is called null field.Under two kinds of different types of cooling, superconducting ring will show different diamagnetisms.For type, high-intensity magnetic field can penetrate superconductor and captured-be called as pinning center by the defective of crystal and crystal boundary.If superconductor is cooled to below the critical temperature in the external magnetic field of closing on, superconductor will be trapped in its inside to the magnetic flux that magnetic patch produces.Will produce the change that suction and repulsion hinder mutual alignment between magnetic patch and the superconductor like this.Promptly can be locked in magnetic patch near certain position in the space superconductor, seem to prick magnetic patch there with nail, therefore is called pinning effect.These instruments used for education are exactly to utilize the pinning effect of superconductor and the demonstration of the super-conductive magnetic suspension that carries out.

When the experiment of demonstration super-conductive magnetic suspension; The present invention adopts high-temperature superconductor ring and magnetic patch to accomplish magnetic suspension experiment; Its effect is significantly different with the traditional super-conductive magnetic suspension experiment effect that uses common solid superconduction piece to be done, and demonstrates the characteristic of high temperature superconducting materia with a kind of mode that is easier to disclose the super-conductive magnetic suspension principle.Magnetic patch in these instruments used for education is a permanent magnet, and permanent magnet can be cylindrical, rectangle or annulus, and the length of permanent magnet is 1～5cm, and permanent magnet can be alloy permanent magnetic material or ferrite permanent-magnet materials, preferred neodymium iron boron magnetic body and ferrimagnet.

The present invention has the following advantages:

The superconducting ring that uses among the present invention is to use the serial high temperature superconducting materia coiling of Bi-2223/Ag.Resistivity and copper conductor the resistivity when temperature be 20 ℃ of this material lead under superconducting state differs 1.75 ten thousand times.Since adopt the multiturn coiling, the induced field that has strengthened induction current so greatly and produced, thus strengthened the interaction force between induced field and the former magnetic field, so the experiment effect highly significant.Stainless steel ring, aluminium ring and copper ring that this external application sectional area is far longer than the superconducting ring sectional area are as a comparison; Resistivity is different; Induction current varies in size, and the induced field size that it produced is also different, and the resistance to former magnetic field of generation is different; Effect comparison is strong, and this helps understanding and understands Lenz law very much.In addition, when the zero resistance characteristic of superconductor has caused the external magnetic field in superconducting ring and becket, to move, the peculiar phenomenon that suffered force direction is incomplete same, so the present invention will help to be familiar with the unusual characteristic of superconductor zero resistance.

The outside textile that is prone to the absorption liquid nitrogen that uses of superconducting ring used in the present invention coats, and can be cotton, burlap, knitting wool, silk or fibers material, adsorbs a certain amount of liquid nitrogen with this and makes coil in the certain hour that breaks away from liquid nitrogen environment, keep superconducting state.Abundant cooled superconducting ring in liquid nitrogen after making it to leave liquid nitrogen, still can make magnetic patch suspend 1～2 minute even longer time, thereby can in the suspension process, move demonstration, has increased sight, interest and the convenience of lecture experiment greatly.

Experimental apparatus of the present invention is simple in structure, and is easy and simple to handle.

Description of drawings

Fig. 1 is these instruments used for education schematic representation of apparatus, wherein:

Stainless steel ring 1, aluminium ring 2, copper ring 3, Dewar 4, superconducting ring 5, magnetic patch 6, bar magnet 7

Embodiment

Embodiment 1

Dewar is kept flat on the table, be placed on superconducting ring in the Dewar 4, stainless steel ring 1, aluminium ring 2, copper ring 3 places respectively on the desktop, makes bar magnet 7 away from superconducting ring 5.

In Dewar 4, add an amount of liquid nitrogen,, avoid liquid nitrogen to spill as far as possible for guaranteeing safety.In the process of cooled with liquid nitrogen superconducting ring and Dewar, can violent boiling phenomenon take place because of a large amount of heat absorptions.Basically stop when seething with excitement, superconducting ring drops to the identical temperature of liquid nitrogen (subzero 196 ℃), promptly gets into superconducting state.This moment, preliminary work was ready, can begin to experimentize.

Successively bar magnet 7 is inserted in stainless steel ring 1, aluminium ring 2 and the copper ring 3 with identical speed; The operator can experience a certain ad-hoc location at different rings; The suffered resistance of bar magnet 7 is obviously different; Bar magnet 7 is inserted in superconducting ring 5 processes, the experimenter can know from experience with insert situation stressed in the becket and variation thereof why not have with.

Bar magnet stressing conditions and bar magnet situation in conductor loops in superconducting ring motion are very different.Its principle Analysis is following:

If making the induction electromotive force that produces in the conductor loops by magnet movement is E.Have according to Faraday's electromagnetic induction law

$E=-N\frac{\mathrm{d\φ}}{\mathrm{dt}}$

Electric current changes the self-induction electromotive force EL that causes in the closed conductor

$E_L=-L\frac{\mathrm{dI}}{\mathrm{dt}}$

If electric current I, resistance R in the conductor.Then, in closed conductor circuit, have according to Kirchhoff's law

$E+E_L-\mathrm{IR}=-L\frac{\mathrm{dI}}{\mathrm{dt}}-N\frac{\mathrm{d\φ}}{\mathrm{dt}}-\mathrm{IR}=0$

In stainless steel ring, aluminium ring, copper ring, generally have

$\left|L\frac{\mathrm{dI}}{\mathrm{dt}}\right|<<\left|\mathrm{IR}\right|$

Therefore have approximately

$\left|I\right|=|\frac{N}{R}\&CenterDot;\frac{\mathrm{d\&phi;}}{\mathrm{dt}}|$

This shows that when magnet moved, suffered resistance was relevant with the resistance of movement velocity, position and conductor in conventional conductor loops.Can find in the experiment, when magnet moves, receive resistance hardly in stainless steel ring, receive smaller resistance when in the aluminium ring, moving, then receive bigger resistance when in copper ring, moving.

Can find in the experiment that the stressing conditions when magnet moves is different fully in the conventional conductor in superconducting ring.The repulsive force that magnet always receives.

This is owing to for superconducting ring, R=0 is arranged approximately.So have

$-L\frac{\mathrm{dI}}{\mathrm{dt}}-N\frac{\mathrm{d\&phi;}}{\mathrm{dt}}=0$

Integration gets

$\left|\mathrm{\&Delta;I}\right|=\left|N\frac{\mathrm{d\&phi;}}{L}\right|$

This shows that magnet moves in superconduction, stressed relevant with the position.In this experiment, from afar near superconducting ring, can think has magnet approximately at the axis of superconducting ring

$\left|I\right|=\left|N\frac{\mathrm{\&phi;}}{L}\right|$

Therefore, when moving on the axis of magnet at superconducting ring, always receive repulsive force; And more near superconducting ring, the electric current in the superconducting ring is just big more.

What in this experiment, pay particular attention to is: magnet always receives repulsive force when on the axis of superconducting ring, moving, and therefore after magnet passes through the superconducting ring central point, can change by force direction.What cause this peculiar phenomenon mainly is the zero resistance characteristic of superconductor, and this is the most important characteristic of this instrument just.

Embodiment 2

The magnetic patch pad is placed on the table, magnetic patch 6 is placed on the top of magnetic patch pad, then Dewar 4 is placed on the desktop, magnetic patch 6 pads are in the hole at Dewar 4 middle parts.Put into Dewar 4 to superconducting ring 5, pour liquid nitrogen then into and cool off.When liquid nitrogen stopped acutely to seethe with excitement, superconducting ring 5 got into superconducting state.Both hands are held Dewar 4 and are left desktop, and at this moment magnetic patch 6 is suspended in Dewar 4 central authorities, along with Dewar 4 moves together.

After Dewar 4 put back to desktop, tie up to slide fastener on the superconducting ring 5 with portable, make superconducting ring 5 leave Dewar 4, at this moment magnetic patch 6 is raised thereupon, is suspended in the circular hole central authorities of superconducting ring 5.Stir magnet 6 with hand, magnetic patch 6 can suspend and rotate.

Take magnetic patch 6 away, and then be put back into superconducting ring 5 belows, magnetic patch 6 still can be suspended in superconducting ring 5 belows.

Claims (11)

1. the instruments used for education of superconducting characteristic of demonstrating comprise superconducting ring, bar magnet, magnetic patch, Dewar, stainless steel ring, aluminium ring, copper ring, Dewar and magnetic patch pad, it is characterized in that superconducting ring processes with the high-temperature superconductor closing coil.

2. instruments used for education according to claim 1; It is characterized in that described closing coil is turned to by hts tape, described superconducting wire is any in the second generation hts tape of YBCO series of Bi-2223 superconducting wire or overlay film.

3. instruments used for education according to claim 1 and 2, the connection that it is characterized in that described closing coil can be to adopt superconduction to connect or welding formation closed-loop path, and connection length is 1～15cm.

4. instruments used for education according to claim 1 is characterized in that can the coiled two cakes of described closing coil, single cake, a plurality of pairs of cakes or solenoidal form.

5. instruments used for education according to claim 1 is characterized in that described closing coil can enclose by coiled more, also can the coiled individual pens, and the line length of using of coil is 5-50m.

6. instruments used for education according to claim 1 is characterized in that the curing of described closing coil is to use epoxy resin or epoxy resin doped aluminium powder to come solidifying and setting.

7. instruments used for education according to claim 1; It is characterized in that described closing coil can use the textile that is prone to the absorption liquid nitrogen to coat; Can be cotton, burlap, knitting wool, silk or fibers material, adsorb a certain amount of liquid nitrogen with this and make coil in the certain hour that breaks away from liquid nitrogen environment, keep superconducting state.

8. instruments used for education according to claim 1; It is characterized in that described bar magnet is made up of permanent magnet and metal bar; It is the rod processed of the ferromagnetic material of 10-20cm or the end of bar that permanent magnet is adsorbed on length; Permanent magnet can be cylindrical, rectangle or annulus, and the length of permanent magnet is 1～5cm.

9. instruments used for education according to claim 1 is characterized in that described magnetic patch is a permanent magnet, and permanent magnet can be cylindrical, rectangle or annulus, and the length of permanent magnet is 1～5cm.

10. according to Claim 8 or 9 described instruments used for education, it is characterized in that described permanent magnet can be alloy permanent magnetic material or ferrite permanent-magnet materials, preferred neodymium iron boron magnetic body and ferrimagnet.

11. instruments used for education according to claim 1; It is characterized in that what described Dewar was processed by thermal insulation material preferably; Can be to process, also can process by metal material parcel thermal insulation material by vacuumizing in the middle of the nonmagnetic substances such as aluminium alloy or stainless steel.

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