4. The
thermal conductivity of superconductors undergoes a continuous change between
two phases. This is usually lower in superconducting state as shown in figure.
5. The
entropy of a superconductor decreases rapidly on cooling below the transition
temperature. This shows that superconducting state is more ordered than the
normal state.
6. All
thermoelectric effect disappear in superconducting state.
7. There
is an appreciable change in the reflectivity of the metal either in the visible
or in the infrared region.
8. The
magnetic characteristics of superconducting state are modified by the addition
of impurities.
9. It
has been observed that critical temperature of semiconductors varies with the
isotopic mass. More precisely, transition temperature is found to vary as the
square root of atomic mass [TC M-1/2].
Q.12 What are the applications of
superconductors?
(AKTU. 2009-10)
Ans. Applications of Superconductors: -
1.
Power Transmission: -
Electrical power transmission
through any conductor is always accompanied by energy loss I2R, where I is the
current and R is the resistance of the conductor. If superconductors are used,
the losses will be eliminated and power transmission can be done at a lower
voltage level.
2.
Superconducting Magnet: -
An electromagnet made by using coils
of superconducting wires or cables is called superconducting magnet. The main
advantage is that once the current is set up, the coil requires no source of
emf to derive the current.
3.
Electrical Applications -
Cryotron: -
Cryotron consists
of a wire of superconducting material A (Tantalum with TC = 4.4 K) around which another wire of
superconducting material B (Niobium with TC =
9.3 K) is wound in the form of solenoid as shown in figure. The wire A is
called as gate.
The cryotron is based on the
principle of disappearance of superconductivity above HC.
4.
Maglev Vehicles: -
When a superconductor magnet is
brought near a permanent magnet, there is a strong repulsive force between
them. This force causes the lighter
