Sample Materials for CSAT Paper -1 (G.S.) Pre 2013: “Science & Technology: Superconductivity”

Sample
Materials From Our Study Notes for CSAT Paper -1 (G.S.) Pre 2013

Subject: Science & Technology:
Topic: Superconductivity

Ques. 1 : What is superconductivity?

Ans. Superconductivity is a phenomenon occurring in certain
materials at low temperatures characterised by complete absence of
electrical resistance and the exclusion of the interior magnetic field (the
Meissner effect).

Superconductivity occurs in a wide variety of materials including simple
elements like tin and aluminium, various metallic alloys, some heavy-doped
semiconductors and certain ceramic compounds containing planes of copper and
oxygen atoms. The latter class of compounds, known as cuprates are also
known as high temperature superconductors (HTs).

Superconductivity does not occur in noble metals like gold and silver nor
in most ferromagnetic metals, although a number of materials displaying both
superconductivity and ferromagnetism have been discovered in recent years.

In 1911, Kammerlingh Ones discovered that a certain temperature, and
often within a narrow temperature range, the electrical resistivity of many
metals and alloys drops suddenly to zero. Ones observed that resistance of
mercury vanishes suddenly at 4.2 k. Conventional superconductors exhibit
superconductivity at relatively lower temperatures. Unconventional
superconductors in particular the high-temperature superconductors (HTs)
superconductor at much higher temperatures (though still far below room
temperature) .

Ques. 2 : Discuss in brief the properties of superconductors?

Ans. Most of the physical properties of super-conductors vary from
material to material, such as the heat capacity and the critical temperature
at which – superconductivity is destroyed. On the other hand, there is a
class of properties that are independent of the underlying material.

1. Zero Electrical Resistance: All superconductors have zero resistivity
to low applied currents when there is no magnetic field present.

2. Critical Temperature T: In superconducting materials, the
characteristics of superconductivity appear when the temperature T is
lowered below a critical temperature To. The value of this critical
temperature varies from material to material.
Conventional superconductors usually have critical temperatures ranging from
less than 1K to around 20 K. Unconventional superconductors such as cuprate
superconductors (e.g. 4Ba2 Cu307) have much higher critical temperature.
4Ba2Cu307 has a critical temperature of 92K. Explanation on how these
materials exhibit superconductivity at higher temperatures is
unsatisfactory.

3. Meissner Effect: When a superconductor is placed in a ‘weak’ external
magnetic field H, the field penetrates the superconductor for only a short
distance \ called the penetration depth, after which it decays rapidly to
zero. This is called the Meissner effect, and is a defining characteristic
of superconductivity. For most superconductors, the penetration depth is of
the order of 100 nm.

The Meissner effect breaks down when the applied magnetic field is too
large. Superconductors can be divided into two classes according to how this
breakdown occurs:

1. Type I Superconductor: In them, superconductivity is abruptly
destroyed when the strength of the applied field rises above critical value
Hc. For example, Most pure elemental superconductors (except vanadium,
niobium, technetium and carbon nanotubes) are type I.

2. Type II superconductor: In Type II superconductors, when the field
applied is beyond a critical value HC1 it leads to a mixed state, in which
increasing amount of magnetic flux penetrates the material, but there
remains no resistance to flow of electric current. But at second critical
field strength, HC2, superconductivity is destroyed.

Applications and uses of Superconductors

I. Medical:

Magnetic resonance imaging
Biotechnical Engineering

II. Electronics:

SQUIDs
Josephson Junction Devices
Particle Accelerators
Sensors
Transistors
Circuitry connections

III Industry

Seperation
Magnets
Sensors and Transducers
Magnetic shielding

IV Transportation

Magnetically levitated vehicles
Marine Propulsion

V Power Generation

Motors
Generators
Energy Storage
Transmission
Fusion
Transformers and Inductors

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Ques. 3 : Give an account of the technological innovations which is
based on supercon-ductivity?

Ans. There have been many technological innovations based on
superconductivity. Superconductors are used to make the most powerful
electro magnets known to man. Super conducting magnets are essential
components of several technologies. Magnetic Resonance Imaging (MR1) is
playing an increasingly important role in diagnostic medicine. The intense
magnetic fields that are needed for these instruments are a perfect
application of superconductors. Similarly, particle accelerators used in
high- energy physics study are very dependent on high field super conducting
magnets.

The field of electronics holds great promise for practical applications
of superconductors. The miniaturisation and increased speed of computer
chips are limited by the generation of heat and the charging time of
capacitors due to the resistance of the interconnecting metal films. The use
of new super-conductive films may result in more densely packed chips which
could transmit information more rapidly by several orders of magnitude.
Super conducting electronics have achieved impressive accomplishments in the
field of digital electronics. Superconductors are used to build Josephson
junctions which are the building blocks of SQUIDs, (Superconducting Quantum
Interference Devices) the most sensitive magnetometers known.

Magnetic-Levitation is an application where superconductors perform
extremely well. Transrport vehicles such as trains can be made to ‘float’ on
strong superconducting magnets, virtually eliminating friction between the
train and its tracks. The conventional electromagnets when compared to
superconductors would waste, much of electrical energy as heat and would be
physically much larger than superconducting magnets. Magnetic Levitation
Trains (MLT) currently exist in Japan and West Germany. MLTs offer an
alternative to air transportation between cities up to a few hundred miles
apart. Japanese MLTs generally run at speeds up to 500 kmph.

The ability of superconductors to conduct electricity with zero
resistance can be exploited in the use of electrical transmission lines.
Currently, a substantial fraction of electricity is lost as heat through
resistance, associated with traditional conductors such as copper or
aluminium. A large-scale shift to superconductivity technology depends on
whether wires can be prepared from brittle ceramics that retain their
superconductivity at higher temperatures (TTK) while supporting large
current densities.

New applications of superconductors will increase with critical
temperature The liquid nitrogen-based superconductors that exhibit
superconductivity at higher temperature has provided industry more
flexibility to utilise superconductivity as compared to ‘conventional’
liquid helium superconductors. The possible discovery of room temperature
superconductors has the potential to bring superconducting devices into our
every day lives.
Promising future industrial and commercial applications include
transformers, power storage devices, motors, electric power transmission,
etc. Most applications today employ the well-understood conventional
superconductors, but it is expected that high- temperature superconductors
will soon become more cost-effective in many cases. The rapid progress in
the field of superconductivity leads one to believe that applications of
superconductors is limited by only one’s imagination and time.

Ques. 4 : Briefly discuss the research developments in the field of
superconduc-tivity?

Ans.
Recognising the importance of promoting superconductivity R&D and
applications in the country, an apex body with Prime Ministers as chairman
and a Programme Management Board (PMB) was constituted in 1987. In February
1991, the National Super conductivity Science and Technology Board (NSTB)
replaced the apex body and the PMB.

The National Superconductivity Programme (NSP) was launched in 1988. In
Phase-I (88-91) 65 projects were started in several institutions including
the leading laboratories in DAE, CSIR, IITs in phase-N (91-95) 6 new
projects were started. The following are the some of the achievements in
superconductivity R&D.

1. High Temperature Liquids: Scientists at National Physical Laboratory (NPL),
New Delhi have developed a new SQUID at Liquid Nitrogen Temperature (UK).
This is considered to be on the high temperature side so far as
superconductors are concerned.

2. Superconducting Magnetic Ore separators: A Superconducting high
gradient magnetic separator (SCHGS) has been developed at BHEL, Hyderabad
with the help of NPL, BARC, Mumbai and National Mineral Development
Corporation.

3. Super Conducting Compound: Monophasic compounds with a critical
transition temperature (Tc of 110 K, 90 K and 80 K have been obtained by the
Department of Nuclear Physics of Madras University.

4. Super Conducting Generator: Engineers at BHEL research centre at
Hyderabad have built arid tested India’s first superconducting generator,
and synchronised it with Andhra Pradesh Power Grid. The achievement has
ushered India into a new era of power generation at ultra low temperature.

Test Your Knowledge

1.Consider the
following statements:

  1. Super conductivity does not occur in
    noble metals like gold and silver.

  2. In 1921, kammerlingh ones discovered that
    a certain temperature and often within a narrow temperature
    range, the electrical resistivity of many metals and alloys
    drops suddenly to zero.

Which of the above statements is/are
true ?

  1. 1 only

  2. 2 only

  3. All of the above

  4. None of the above

 

1.Consider the
following statements

  1. Conventional superconductors usually have
    critical temperatures ranging from less than 1k to around 10
    k.

  2. Ceramic compounds containing planes of
    copper and oxygen atoms known as cuprates.

Which of the above statements is/are
true ?

  1. 1 only

  2. 2 only

  3. All of the above

  4. None of the above

 

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Answer of Question 1: A

Answer of Question 2: B


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