PHY_10_51_V1_TG_Superconduct

RECOMMENDATIONS

on lesson “Superconductivity and its application”

In this lesson students supposed to work with computers. However id there is not available computers that teachers can use in physics class three videos can be watched one by one. Videos are short, so it possible to do it in one lesson. While students presenting their ideas teacher might assess each group according to the poster rubrics:

There is a useful arcticle about the physics of superconductivity:

Physicists discover flaws in superconductor theory

This image of a magnet levitated over a high-temperature superconductor array shows rectangular TFMs (black) levitating a heavy ferromagnet (silver) above a container of liquid nitrogen.

The basic property of superconductors is that they represent zero "resistance" to electrical circuits. In a way, they are the opposite of toasters, which resist electrical currents and thereby convert energy into heat. Superconductors consume zero energy and can store it for a long period of time. Those that store magnetic energy —known as "trapped field magnets" or TFMs—can behave like a magnet.

In the Journal of Applied Physics, the researchers describe experiments whose results exhibited "significant deviations" from those of the Critical State Model. They revealed unexpected new behavior favorable to practical applications, including the possibility of using TFMs in myriad new ways.

Much of modern technology is already based on magnets. "Without magnets, we'd lack generators [electric lights and toasters], motors [municipal water supplies, ship engines], magnetrons [microwave ovens], and much more," said Roy Weinstein, lead author of the study, and professor of physics emeritus and research professor at the University of Houston.

Generally, the performance of a device based on magnets improves as the strength of the magnet increases, up to the square of the increase. In other words, if a magnet is 25 times stronger, the device's performance can range from 25 to 625 times better.

TFMs are clearly intriguing, but their use has been largely held back by the challenge of getting the magnetic field into the superconductor. "A more tractable problem is the need to cool the superconductor to the low temperature at which it super conducts.

"Bean assumed the superconductor had zero resistance and that the basic laws of electromagnetism, developed circa 1850, were correct," Weinstein said. "And he was able to predict how and where an external magnetic field would enter a superconductor."

The method widely used today is to apply a magnetic field to a superconductor via a pulse field magnet after the superconductor is cooled. Bean's model predicted, and until now experiments confirmed, that to push as much magnetic field as possible into a superconductor, the pulsed field must be at least twice as strong, and more typically over 3.2 times as strong, as the resulting field of the TFM.

But, this severely limits the applicability of TFMs. "It's difficult and expensive to produce fields of more than 12 tesla," said Weinstein. "If Bean's theory held true, this cost and practicality barrier would limit TFMs used within products to a maximum of typically 3.75 tesla."

Minor problems with Bean's Critical State Model emerged shortly after it was published, according to Weinstein. Any chink in theoretical armor is worthy of an exploratory experiment, and this is what motivated Weinstein and his colleagues.

They discovered that for certain constraints on a magnetic pulse, Bean's model is far off base, and a significantly different spatial distribution of field occurs. "Great increases in field occur suddenly, in a single leap, whereas Bean's model predicts a steady, slow increase," Weinstein said.

"By using our newly discovered methods, the maximum TFM field is now 12 tesla," said Weinstein. "A motor, if made in a fixed size, can produce 3.2 times the torque. Alternatively, the motor can be designed to produce the same amount of torque, but have its volume reduced by more than 10 times. This reduction in materials can result in great cost savings."

The researchers are still within the "early days" of this work and have already disproven their first thoughts concerning what is causing their results. "We're now essentially spelunking in a dark cave without lights—it's frustrating, but exciting," Weinstein said.

In terms of applications for their discovery, the researchers suggest the ability to replace a $100,000 low-temperature superconducting magnet in a research X-ray machine with a $300 TFM, or possibly replace a motor with one that is a quarter of the size of an existing one. There are many other potential applications, such as an energy-efficient ore separator, noncontact magnetic gears that will not wear or require repair, a red blood separator with 50 percent improved yield, and even an automated docking system for spacecraft.

Weinstein and colleagues are now searching for fast, short-term support that will allow them to continue their research to explain this new phenomenon. "While we now know enough to apply our new discovery to significantly improve a large number of devices, we don't yet fully know what's going on in terms of the basic laws of physics.

Additional multiple choice questions with answers on topic Superconductors

1.    What happens to current sent through a superconducting wire?

A) It gains a slight voltage boost.

B)  It's transmitted without loss of energy.

C)  It experiences a sharp voltage drop.

Superconductors have zero resistance, so current sent through such a wire loses no energy.

2.Who discovered superconductivity?

A) Johannes Diderik van der Waals

B)  Hugo Christiaan Hamaker

C)  Heike Kamerlingh Onnes

Dutch physicist Heike Kamerlingh Onnes and his collaborators, Cornelis Dorsman, Gerrit Jan Flim and Gilles Holst discovered superconductivity. The research of Johannes Diderik van der Waals -- a fellow countryman and contemporary physicist famous for the forces, molecules, radii and equation of state that bear his name -- helped inspire Onnes’ work. Hugo Christiaan Hamaker, another Dutch scientist, was an experimental physicist famous for his statistical work.

2.    In what year did Onnes discover it?

A)    1911

B)    1921

C)    1931

When it was first identified by Dutch physicist Heike Kamerlingh Onnes in 1911, superconductivity flew in the face of established physics. In fact, an entirely new kind of physics, quantum mechanics, would have to be established before anyone had a hope of cracking the mystery of how the phenomenon worked.

3.    Approximately how cold do conventional superconductors have to get before they enter the superconducting state?

A) 0 K (minus 273.2 C, minus 459.7 F)

B)  39 K (minus 234 C, minus 390 F)

C)  130 K (minus 143 C, minus 226 F)

Superconductors only function at very cold temperatures, on the order of 39 K for conventional superconductors (the solid mercury wire that Kamerlingh Onnes used had to be cooled below 4.2 K) and below around 130 K for modern, high-temperature superconductors. As for absolute zero, it cannot be achieved artificially, although laser cooling has taken us within one billionth of a degree of it.

4.    Superconductors cease being superconductors if they are exposed to which of the following?

A) too large of a magnetic field

B)  too much current

C)  Both are correct.

Just as superconductors have a critical temperature that separates them from normal conductors, they also have a critical magnetic field that hits them like kryptonite. Too much current will also take superconductors from hero to zero.

5.    Which of the following do NOT currently use superconductors?

A) MRI machines

B)  alkaline batteries

C)  proton accelerators

Although low critical magnetic fields limited the usefulness of older Type I superconductors for magnetic applications, modern Type II superconductors, such as niobium-titanium (NbTi), can handle much higher magnetic loads. Because they produce higher magnetic fields than, say, electromagnets made from copper wire, they have proven invaluable in MRI machines and proton accelerators.

6.    How well a material conducts electricity has to do with what factor?

A) how easily its component atoms give up electrons

B)  the availability of free electrons to carry current

C)  both A and B

Good electrical conductors have atomic structures that readily give up electrons, moving them from the valence energy level to the conductance energy level. The result is a large number of free electrons available to carry current. Thus, the two answers essentially describe the same thing.

7.    You can describe the structure of a typical conductor as which of the following?

A) a lattice of atoms

B)  a series of tubes

C)  a bevy of bosons

A conductor is composed of a lattice of atoms, like a tiny jungle gym in which the intersections represent atoms and the connecting rods stand in for interactive forces. A bevy of bosons would be a boon to behold, but bears no relation to a typical conductor. Thanks to Alaskan Sen. Ted Stevens, everyone knows that the Internet is a series of tubes.

8.    What of the following is NOT a source of resistance in a typical conductor?

A) deformation

B)  cold

C)  heat

The more deformed the lattice of the material is, the more likely it is that it will interfere with the free flow of electrons. The same is also true for higher temperatures, which cause the lattice and its component atoms to vibrate and oscillate faster. Cold, as a rule, decreases resistance.

9.    What happens to a superconductor when it is cooled to its critical temperature?

A) It abruptly loses all resistance.

B)  It undergoes a phase transition.

C)  Both are correct

D) Wrong Answer!

As a superconductor is cooled, its resistance gradually drops until the critical temperature is reached, after which all resistance abruptly disappears. The substance has undergone a phase transition from conventional material to superconductor.

10.              What are Cooper pairs?

A) elements on the periodic tale that share the same conductance

B)  pairings of metals that make good superconducting alloys

C)  linked electrons that help explain superconductivity

In a superconductor, two electrons pair off to gain a net advantage when dealing with the ions that make up the material lattice. As the electron passes through the positively charged lattice, it attracts the surrounding atoms toward it. As they bunch up, these atoms create a local area of higher positive charge, which increases the force pulling the second electron forward. Consequently, the energy spent to get through, on average, breaks even.

11.              What is the name of the theory that explains how conventional superconductors work?

A) the XTC theory

B)  the BCS theory

C)  the Aquitaine Progression

Superconductors were known for almost half a century before, in 1957, physicists John Bardeen, Leon N. Cooper and John Robert Schrieffer finally advanced a theory that worked. In their honor, this fundamental theory of superconductivity is generally known as the Bardeen-Cooper-Schrieffer, or BCS, theory. In case you're wondering, XTC was a New Wave band from Swindon, England, and "The Aquitaine Progression" was a book by Robert Ludlum, but it sounded cool.

12.              Today, superconductors that fit the BCS model are called "classical." What's the designation for superconductors that do NOT jibe with this theory?

A) exotic

B)  strange

C)  top

Within a decade or two of the BCS theory being published, researchers began discovering other superconductors, such as heavy-fermion systems and high-temperature superconducting cuprates that broke the model. Today, superconductors that fit the BCS model are called “classical,” while those that don’t are known as "exotic." The means by which these exotic superconductors operate remains the subject of hot debate. "Strange" and "top" are designations used to describe quarks.

13.              Which of the following elements become superconductors at low temperatures and pressures?

A) selenium, silicon and uranium

B)  aluminum, lead, mercury and tin

C)  chromium, cobalt, iron, manganese and nickel

Hundreds of materials, including 27 metallic elements -- such as aluminum, lead, mercury and tin -- become superconductors at low temperatures and pressures. Another 11 chemical elements -- including selenium, silicon and uranium -- transition to a superconductive state at low temperatures and high pressures. The magnetic elements chromium, cobalt, iron, manganese and nickel are not superconductors.

14.              Most superconductors are what type of material?

A) alloys or compounds

B)  metallic elements

C)  metalloids

The vast majority of superconductors are alloys or compounds.

15.              Which type of superconductor exhibits perfect diamagnetism in every superconducting state?

A) Type I

B)  Type II

C)  both of the above

When cooled below its critical temperature, a Type I superconductor not only exhibits zero electrical resistivity, it also displays perfect diamagnetism. Type II superconductors display perfect diamagnetism while in one superconducting state but not in the other.

Useful resources:

https://play.howstuffworks.com/quiz/superconductivity-quiz

http://mriquestions.com/superconductivity.html

http://chabanoiscedric.tripod.com/NSCHSS.PDF

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