Q.1 What is superconductivity? Discuss the
temperature dependence of resistivity in superconducting materials.
Ans. Superconductivity: -
When a substance loses its
electrical resistance, i.e., a current can continue through it without changing
its value, the phenomenon is known as superconductivity.
or, When the electrical resistance of a
substance drops suddenly to zero, when it is cooled below a certain
temperature, the phenomenon is known as superconductivity.
Temperature
Dependence of Resistivity In Superconducting Materials: -
The dependence of resistivity of a superconductor is shown
in figure. The resistance of the superconductor in non superconducting state
decreases with decrease in temperature as in case of normal metal. But at a
particular temperature TC, the resistivity abruptly drops to zero.
TC is called as critical temperature. Therefore, the
temperature at which a normal material turns into a superconductor is called as
critical temperature. The critical
temperature is different for different conductors.
Q.2 Explain Meissner effect. Give the
experimental demonstration of Meissner effect.
Related
Questions -
Q. Describe Meissner effect in
superconductors. (AKTU. 2011 - 12, 12 - 13)
Ans. Meissner Effect (Flux Exclusion): -
Meissner in 1933 observed that
if a superconductor is cooled in a magnetic field, below critical temperature
corresponding to that field, then the lines of induction are expelled from the
material. This effect is called as Meissner effect.
Figure (a) shows a superconductor in
normal state and the magnetic lines of force pass through it. But when the
specimen is cooled below its transition temperature figure (b), the magnetic
lines of force are expelled out of the specimen.
There are
some important points for the Meissner effect given as follows –
1. Meissner
effect is reversible.
2. A
superconductor is a perfect diamagnetic.
3. The
difference between a perfect conductor and superconductor is that the former is
only an ideal conductor while the later is simultaneously an ideal conductor
and an ideal dimagnet.
Demonstration
of Meissner Effect: -
As shown in the figure two coils one primary and other secondary
are wound on a superconductor. The superconductor is above its critical
temperature. In primary circuit, there is a battery B and tapping key K. The
secondary coil is connected to a galvanometer.
When the key K is pressed, a
current flows through the primary coil. This sets up a magnetic field in
primary coil. The magnetic flux immediately links with the secondary coil. As a
result, the galvanometer shows a momentary deflection. After that the primary
current becomes steady. Now no current flows in the secondary.
Now, the temperature of
superconductor is decreased gradually. As soon as the temperature crosses below
the critical temperature, the galvanometer shows a deflection. This indicates
that the flux linkage with the secondary coil has changed. The change in
magnetic flux is due to expulsion of magnetic flux from superconducting
material. This shows the experimental demonstration of Meissner effect.
Q.3 What are super conductors? (AKTU. 2012 - 13)
Related
Questions -
Q. What are type I and type II
superconductors? Explain.
(AKTU. 2008-09)
Q. What are superconductors? Explain their classification as
type I and type II superconductors. (AKTU. 2010 - 11)
