# Applied Physics-May/June 2008

1. (a) Plot and explain the variation of (i) attractive potential energy (ii) repulsive potential energy and (iii) resultant potential energy with inter-atomic distance, when two atoms are brought nearer.
(b) The Madelung constant of KCl is 1.75. Its neighbour separation is 0.314 nm. Find the cohesive energy per atom. [Given that the Repulsive exponent value= 5.77; Ionization energy of potassium = 4.1 eV; Electron affinity of chlorine= 3.6 eV]
2. (a) Discuss the de Broglie hypothesis of duality of matter particles.
(b) Describe GP Thomsons experiment to verify the wave nature of matter.
3. (a) Explain the terms (i) mean free path, (ii) relaxation time and (iii) drift velocity of an electron in a metal.
(b) Discuss the origin of electrical resistance in metals.
(c) Calculate the mobility of the electrons in copper obeying classical laws. Given that the density of copper = 8.92 × 103 kg/m3, Resistivity of copper = 1.73 ×10?8 ohm-m, atomic weight of copper = 63.5 and Avogadro’s number = 6.02 ×1026 per k-mol.
4. (a) Describe the phenomenon of electronic polarization and obtain an expression
for electronic polarizability.
(b) Write notes on:
i. Ferro-electricity and
ii. Piezo-electricity.
5. (a) Write a note on intrinsic semiconductors.
(b) Derive an expression for the carrier concentration in n-type extrinsic semi-conductors.
6. (a) Distinguish between spontaneous emission and stimulated emission.
(b) Distinguish between homo-junction semiconductor laser and hetero-junction semiconductor laser.

(c) Calculate the wavelength of emitted radiation from GaAs which has a band gap of 1.44 eV.
7. (a) What are important features of optical fibers?
(b) Describe the communication process using optical fibers.
(c) Write the uses of fiber optics in different fields.
8. (a) Write a detailed note on nanoscience and nanotechnology.
(b) Write the important applications of nanomaterials in medicine.