Physics — Winter 2019

Explain Drude model

Fermi energy of a given substance is 7.9 eV. What is the average energy and speed of electron in this substance at 0 K?

Explain photovoltaic effect. With required diagrams discuss construction and working of solar cell.

Write a short note on exciton.

Consider two-dimensional square lattice of side 3.0 Å. At what electron momentum values do the sides of first Brillouin zone appear? What is the energy of free electron with this momentum?

Derive an equation of joint density of states.

Define Hall effect. Give its physical significance.

2.0Cm wide and 1.0 mm thick copper strip is placed in a magnetic field 1.5Wb/m2 perpendicular to the strip. Suppose a current of 200A is set up in the strip what will be the Hall potential appeared across the strip? (n=8.4x1028 electrons /m3).

Discuss UV-VIS method for band gap measurement of semiconductor.

Discuss Fermi golden rule.

The transmitted intensity is 0.4 times intensity of incident light. If this light is incident on a semiconductor having a thickness of 0.5cm then find absorption coefficient.

Explain four probe method. Derive an equation to calculate resistivity of a thin sample.1

Write short note cryotron.

Explain London’s penetration depth.

Give the difference between type 1 and type 2 superconductor.

Write short note on SQUID.

Calculate the critical current for a superconducting wire of lead having a diameter of 2 mm at 2 K. Critical temperature for lead is 4 Kand Hc (0) = 6.5 X 104 A/m.

Explain the properties of superconductors in detail.