9.8 Superconductivity  (Page 5/12)

Describe two main features of a superconductor.

How does BCS theory explain superconductivity?

What is the Meissner effect?

What impact does an increasing magnetic field have on the critical temperature of a semiconductor?

At what temperature, in terms of $T_C$ , is the critical field of a superconductor one-half its value at $T=0\text{K}$ ?

What is the critical magnetic field for lead at $T=2.8\text{K}$ ?

A Pb wire wound in a tight solenoid of diameter of 4.0 mm is cooled to a temperature of 5.0 K. The wire is connected in series with a $50\text{-}\text{Ω}$ resistor and a variable source of emf. As the emf is increased, what value does it have when the superconductivity of the wire is destroyed?

A tightly wound solenoid at 4.0 K is 50 cm long and is constructed from Nb wire of radius 1.5 mm. What maximum current can the solenoid carry if the wire is to remain superconducting?

Potassium fluoride (KF) is a molecule formed by an ionic bond. At equilibrium separation the atoms are $r_0=0.255\text{nm}$ apart. Determine the electrostatic potential energy of the atoms. The electron affinity of F is 3.40 eV and the ionization energy of K is 4.34 eV. Determine dissociation energy. (Neglect the energy of repulsion.)

For the preceding problem, sketch the potential energy versus separation graph for the bonding of ${\text{K}}^{+}\text{and}{\text{Fl}}^{\text{−}}$ ions. (a) Label the graph with the energy required to transfer an electron from K to Fl. (b) Label the graph with the dissociation energy.

The separation between hydrogen atoms in a ${\text{H}}_2$ molecule is about 0.075 nm. Determine the characteristic energy of rotation in eV.

The characteristic energy of the ${\text{Cl}}_2$ molecule is $2.95\times {10}^{\mathrm{-5}}\text{eV}$ . Determine the separation distance between the nitrogen atoms.