Chapter 43, Problem 1OQ

To determine

True statements among the following statements about a superconductor below its critical temperature.

Answer to Problem 1OQ

(a)        False

(b)        False

(c)        True

(d)        True

(e)        True

Explanation of Solution

(a)

A super conductor is a material that offers zero resistance to the passage of electrons. It exhibits superconductivity below a particular temperature called critical temperature. They also expels all the magnetic flux lines.

When the temperature of a super conductor is reduced beyond its critical temperature, all the magnetic field lines from the conductor will be expelled. So if the super conductor carried infinite current, it would produce infinite magnetic field which is against the theory of super conductors. Hence statement (a) is $\underset{\_}{\text{False}}$.

(b)

A conductor becomes super conductor if the temperature is reduced below the critical temperature of the conductor. A condition that they should carry some non-zero current in it does not exist. So statement (b) is $\underset{\_}{\text{False}}$.

(c)

Write the expression for resistivity of a conductor.

    $\rho =\frac{E}{J}$

Here, $\rho$ is the resistivity of a conductor, $E$ is the electric field, and $J$ is the current density.

For a superconductor under critical temperature, the resistivity is zero. From the above equation, if resistivity has to be zero, then electric field must be zero. Thus option (c) is $\underset{\_}{\text{True}}$.

(d)

When the temperature of a conductor is reduced below its critical temperature, resistance reduces to zero and all the magnetic field lines inside the conductor is expelled. Then the conductor is said to be a super conductor. When the temperature is lowered, the electrons will rearrange themselves to make the net magnetic field equal to zero. Thus option (d) is $\underset{\_}{\text{True}}$.

(e)

For internal energy to be produced, the charge carriers should collide with the lattice ions. For normal conductors the charge carriers while moving collide with the lattice and produce energy. But in super conductor the current is carried by cooper pairs. But cooper pairs never collide with lattice as they remain in pairs. So internal energy is produced. Thus option (e) is $\underset{\_}{\text{True}}$.