Physics — Summer 2025

Write short note on: Phonon.

Derive formula of fermi energy level for N-type semiconductor.

Evaluate Fermi function (or occupation probability) for energy 2k Tabove B the Fermi energy.

Derive formula of diffusion current density for electron as well as hole.

Discuss forward bias and reverse bias for a PN junction diode and draw characteristics curve.

Discuss Fermi golden rule for transition probability.

Explain in detail experimental procedure for DLTS.

Discuss direct and indirect band gap semiconductors.

State any three points of differences between spontaneous emission and stimulated emission.

(i) What is called exciton? (ii) Name two metal-semiconductor junctions. (iii) What is called optoelectronic device?

The electrical conductivity (σ) of copper at 300 Kis 6.2 × 107 Ω–1 m–1. Calculate the thermal conductivity of copper. Lorentz number is 2.44 × 10– 8 W/K2.

Discuss in detail UV-VIS method for band gap measurement of semiconductor.1

What is Meissner effect? For superconductor show that χ = –1. m

Write any four points of comparison of type-Iand type-II superconductor.

(i) Calculate the critical current for a superconducting wire having radius of 0.2 mm at 5 K. Critical temperature of material of wire is 7.2 Kand Hc (0) is 2.2 × 104 A/m. (ii) For a superconducting material isotopic mass is 195 amu and critical temperature is 5.2 K. Calculate isotopic mass at 6.5 K.

Write a short note on: SQUID

What is superconductivity? Discuss any three properties of superconductor.

Discuss in detail four-point probe method for the measurement of resistivity.