Physics — Winter 2023

Mention any three postulates of classical free electron theory proposed by Lorents and Drude.

(i) State any two points of differences between intrinsic and extrinsic semiconductors. (ii) State any two points of differences between n-type and p-type semiconductors.

What is superconductivity? Discuss any three properties of superconductors in detail.

Obtain Fermi factor f (E) for energy 0.01 eV above Fermi energy (E) at 500 f K.

State and discuss Wiedemann-Franz law.

Define density of states and derive its expression.

What is E-k diagram? Discuss direct and indirect band gap semiconductors based on E-k diagram.

(i) Write fermi distribution function and mention physical significance of it. (ii) Mention any two applications of solar cell.

Derive formula of drift and diffusion current densities.

(i) Draw characteristic curve for p-n junction diode. (ii) Discuss forward bias characteristics with proper circuit diagram. (iii) Discuss reverse bias characteristics with proper circuit diagram.

Apotential barrier of 0.6 Vexists across of p-n junction. The intensity of the electric field in this region is 2.4 106 V/m. Find the width of depletion region.

(i) Mention any two applications of LED. (ii) Calculate the value of band gap for a LED for the emission of blue light of wavelength 452 nm. (h = 6.63 10‒34 Js, c = 3 108 m/s)

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

(i) What is called optoelectronic device? (ii) Name the types of metal-semiconductor junction.1 (iii) What is called exciton?

Discuss Frenkel and Wannier-Mott exciton in brief.

What is photovoltaic effect? Explain construction and working of solar cell in detail.

(i) What is Hall effect? (ii) The Hall coefficient of a semiconducting material is 2.4 10‒4 m3/C. Calculate the mobility and carrier concentration of the carrier if resistivity is 6 10‒3 Ω m.

Discuss Fermi’s golden rule for transition probability.

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

Calculate the critical current through a long thin superconducting wire of radius 10–3 m. The critical magnetic field is 6.2 103 A/m.

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

Discuss in detail experimental procedure for DLTS.

The critical temperature of a superconductor is 7.5 K. Calculate the critical field at 5 K. At 0 Kthe critical field is 0.24 T.

Write a short note on London penetration depth.

(i) Discuss BCS theory of superconductivity in brief. (ii) Draw constructive diagram of SQUID and mention its application.