Superconductors

This resource introduces some complex formulae and shows superconductors work in the same way as the simple formulae students are used to.

The material also offers the opportunity for a discussion of the concept of ‘blue skies’ research.

Notes

The activity could be introduced by showing students a video clip illustrating the levitation properties of superconductors.

There are some good, short clips on http://www.fys.uio.no/super/levitation/ (accessed December 2005).

A list of uses of superconductors is given in the student material. You may prefer to ask students to research this for themselves.

There is a very good section on the website http://www.superconductors.org (accessed December 2005), which would be an excellent starting point for their research.

The site has details of several uses and potential uses of superconductors and provides links to other related web pages. Students could research one use and produce a poster on it. The posters could then be shared and discussed with the whole class.

Ask students to think about the advantages and disadvantages of superconductors for each application. Some students may be interested in how superconductors work.

The above superconductors’ website has some good, clear explanations of this, particularly at http://www.superconductors.org/oxtheory.htm (accessed December 2005).

Blue skies research

These questions are designed to stimulate discussion, rather than requiring full written answers. Examples of discoveries that have been made by chance or when researchers were looking for something else include the glue in Post-it® notes (scientists were searching for a strong glue), polythene and Teflon®.

The discovery of the hole in the ozone layer is an example of something that was missed by those with the most data. The credit for the discovery went to Molina and Rowland in the mid-80s but NASA had relevant data right back to the mid-1970s.

However, NASA scientists missed the discovery because their data had not been properly analysed. There are more details on this story on the NASA website http://www.nas.nasa.gov/About/Education/Ozone/history.html (accessed December 2005)

Questions

1. What is a conductor? Which type of substance usually conducts when solid?
2. What is a superconductor?
3. What would be the main advantage and the main disadvantage of using superconductors for power cables?
4. How long was it from the discovery of superconductivity until it was first used commercially?
5. Why is it surprising that a giant ionic compound can behave as a superconductor? (Use ideas about structure and bonding in your answer.)
6. Explain why helium is so much more expensive than nitrogen. Give two reasons.
7. Use a Periodic Table to find out the names of the elements in YBa₂Cu₃O₇. How many atoms of each element are present in this material? Can you suggest what it might be called?
8. Why were scientists excited to find that the Tc of this compound was above -196 °C?
9. Use a Periodic Table to find out what the elements in the material shown are called.

Answers

1. A conductor is a substance that conducts heat or electricity. Metals usually conduct when solid.
2. A superconductor is a substance that conducts electricity without any resistance.
3. Advantage – no loss of energy. Disadvantage – high cost of cooling with liquid helium.
4. From 1911 to 1962 – 51 years.
5. Giant ionic compounds do not conduct when solid as they have no free electrons or other charged particles that can move to carry the current. As they do not ordinarily conduct, it is surprising to find them behaving as superconductors.
6. Nitrogen is far more common. Also, since nitrogen has a higher boiling point than helium, less pressure is needed to liquefy it, which means less energy is required to produce liquid nitrogen.
7. Yttrium, 1 atom; barium, 2; copper, 3; oxygen, 7. This compound is called yttrium barium copper oxide (but is usually referred to as YBCO).
8. The compound could be made to superconduct by cooling in liquid nitrogen, which is a lot cheaper than liquid helium.
9. The material contains mercury, thallium, barium, calcium, copper, oxygen.

Uses of superconductors

Superconductors are used in the following applications:

• Maglev (magnetic levitation) trains. These work because a superconductor repels a magnetic field so a magnet will float above a superconductor – this virtually eliminates the friction between the train and the track. However, there are safety concerns about the strong magnetic fields used as these could be a risk to human health.
• Large hadron collider or particle accelerator. This use of superconductors was developed at the Rutherford Appleton Laboratory in Oxfordshire, UK in the 1960s. The latest and biggest large hadron collider is currently being built in Switzerland by a coalition of scientific organisations from several countries. Superconductors are used to make extremely powerful electromagnets to accelerate charged particles very fast (to near the speed of light).
• SQUIDs (Superconducting QUantum Interference Devices) are used to detect even the weakest magnetic field. They are used in mine detection equipment to help in the removal of land mines.
• The USA is developing “E-bombs”. These are devices that make use of strong, superconductorderived magnetic fields to create a fast, high-intensity electromagnetic pulse that can disable an enemy’s electronic equipment. These devices were first used in wartime in March 2003 when USA forces attacked an Iraqi broadcast facility. They can release two billion watts of energy at once.

The following uses of superconductors are under development:

• Making electricity generation more efficient
• Very fast computing.

Other impacts of superconductors on technology will depend on either finding superconductors that work at far higher temperatures than those known at present, or finding cheaper ways of achieving the very cold temperatures currently needed to make them work.

Scientific research that does not have a particular commercial aim in view is called blue skies research. Many discoveries are made ‘by chance’ when scientists are trying to find out something else.

The discovery of superconductivity was made nearly 100 years ago but technological applications have really only become available in the last 10 years or so. Think about the following questions and discuss them with others:

• Is it important that blue skies research is carried out?
• Who should fund it?
• Why is it important that scientists record all their observations – even ones which do not fit the pattern they were expecting?
• Do you know of any scientific developments that were made by chance – maybe when the researchers concerned were looking for something else?