Superconductors

Superconductors PH1.5 Resistance

SuperconductorsSuperconductors are relatively were discovered in 1911, but not much has been known about them until recently, and still there is a lot more research into superconductors to come.

Superconductor are materials that has zero resistance. Therefore there is a lot of fuss about them because they can be very useful. If they have zero resistance energy will not be lost when passing a current through the material.

Transition TemperatureThe transition temperature is the temperature at which a material, when cooled loses all its electrical resistance and becomes superconducting.

Typical transition temperatures;

(you need not know these but they are here to give you an idea how cold a material must be before it becomes a superconductor)

You must note that not all materials become superconductors (eg Copper). No matter how low the temperature they will never become a superconductor.

High Temperature SuperconductorsA high temperature superconductor is one that has a transition temperature above 77K (-196°C). This is the boiling point of nitrogen.

The materials are cooled to their transition temperature by using liquid nitrogen.

As of yet no superconductor has been found with a transition temperature even close to room temperature.

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Material

Transition Temperature

(K)Zinc 0.88

Aluminium

1.19

Tin 3.72

Mercury 4.15


Graph of a superconductor

Uses of Superconductors Magnetic Levitation – trains that levitate above the track,

because they aren’t in contact with the track there is no energy lost in heat and friction, therefore they can achieve very high speeds

MRI Scans – used to see inside the body by doctors. Particle Colliders – such as in Switzerland superconducting

materials are used to accelerate the particles for the speeds needed.

Key Points A superconductor is a material that has zero resistance The transition temperature is the temperature at which a

material, loses all its resistance and becomes superconducting. Not all materials can be a superconductor Know some of the uses of superconductors

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Key Point; New uses are constantly being found superconductors. If

you know a use not mentioned here you will still get the mark on the exam. Examiners have to check out the uses on the internet, as they are ever changing.


Practice Questions1. What is a superconductor? (1 mark)

2. With the aid of a sketched graph explain the term superconducting transition temperature (3 marks)

3. Explain why superconductors are useful for applications which require large electric currents and name one such application. (2 marks)

4. Explain the term high temperature superconductor (1 mark)

5. How are materials cooled to their critical temperatures? (1 mark)

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(WJEC June 2010)

(WJEC June 2010)

(WJEC June 2010)


Worked Answers1. A material which has zero [electrical] resistance [or equiv.] [1]

2.

3. Little energy/heat lost. MRI scans, magnetic levitation, particle accelerators, nuclear fusion.

4. A material with a transition temperature above 77K/-196°C

5. Using liquefied gases/ liquid nitrogen.

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Mark Scheme; 1 mark for correct axis. 1 mark for correct

shape of line (must be sudden drop to 0Ω).

1 mark for labelling transition temperature or describing this is where the line drops.

Mark Scheme; 1 mark for little

energy/heat lost. 1 mark for any

acceptable use


Robert Williams – December 2011

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Superconductors