BSc Physics SEM V ATKT PHYSICS PAPER II SOLID STATE PHYSICS Question Paper - Mumbai University | munotes

Questions asked in this paper

• (2) Figures to the right indicate full marks

1. Q1 (a) Attempt any one:
   • (i) Derive the expression for interplaner distance between two 10 consecutive planes in simple cubic crystal system
   • (ii) On the basis of classical electron theory explain the terms relaxation 10 time and mean free path. Derive expressions for relaxation time in terms of drift velocity
   • (b) Attempt any one:
   • (i) Derive the expression for the atomic packing factor of body centered 5 cubic crystal with help of neat diagram
   • (ii) Calculate the lattice constant for — iron with bec structure. 5 [Given: Density of 7.86 x 10%kg/m?
2. Q2 (a) any one:
   • (i) Explain the Brillouin zones in one dimension and two dimensions 10 with neat diagram. How are they related to the energy levels of an electron in a solid?
   • (ii) Kronig — Penney model for the motion of an electron in 10 periodic potential. Thus explain the band theory for solids
   • (b) Attempt any one:
   • (i) Show how F(E). varies with energy for a metal at T= 5
   • (ii) Obtain the expression between mean energy of electron gas in terms 5 of Fermi energy at absolute zero Paper Subject Code: 24126 Physics : Paper II - Solid State Physics. (R-2017)
3. Q3 (a) Attempt any one:
   • (i) Derive the expression of concentration of electrons in conduction 10 band for an intrinsic semiconductor. Hence state the expression for hole concentration in its valance band
   • (ii) Explain the concept of carrier lifetime. Set up the continuity equation 10 for the charge carriers in a semiconductor
   • (b) Attempt any one:
   • (i) What is p-n junction diode? Draw the energy level diagram of p-n 5 junction and explain why a contact potential difference is developed across an unbiased p-n junction
   • (ii) The energy gap of silicon is 1.1 eV. Its electron and hole mobilities 5 at room temperature are 0.48 and 0.013 respectively Calculate its conductivity. For Si, x /m?
4. Q4 (a) Attempt any one:
   • (i) Derive the expression for volt-ampere characteristic of p-n junction 10
   • (ii) What is the Meissner effect? Explain the effect of magnetic field on 10 superconductivity. What do you mean by the penetration depth in relation to superconductivity?
   • (b) Attempt any one:
   • (i) What is paramagnetism? Explain the origin of permanent magnetic 5 dipole due to orbital motion of an electron
   • (ii) Calculate the static and dynamic resistance of a germanium p-n 5 junction diode, at room temperature of 27 if its reverse saturation current is A and a forward bias of 0.2 volts is applied to it
5. Q5 (a) Attempt any one:
   • (i) Draw (11 2 3)and (2 0 0) planes for simple cubic 4
   • (ii) The resistivity of aluminium at room temperature is 2.62 X 4 ohm.m. Calculate relaxation time on the basis classical free electron theory. Density of
   • (b) any one:
   • (i) Using the Fermi-Dirac distribution function obtain the value of 4
   • (ii). Calculate the total number of states below E = 5 eV in a metal of 4 volume m3. Assume the electrons to be free Paper Subject Code: 24126 Physics : Paper II - Solid State Physics. (R-2017)
   • (c) Attempt any one:
   • (i) Compare the densities of charge carriers in a pure germanium 4 crystal at the temperatures 300 K and 320 K. The energy gap for germanium is 0.7 eV
   • (ii) For Ge p-n diode, Np= 10* Na and Na is corresponding to 1 acceptor 4 atom per Ge atoms. Calculate the barrier height Eo in eV at room temperature. For Ge, ni= 2.15 x and atomic density is 4.42
   • (d) Attempt any one:
   • (i) Calculate the value of applied forward voltage for a p-n junction 3 diode if I= forward current I= 2A and e/KT=40 per volt
   • (ii) A paramagnetic substance has magnetic moment 3 of each atom is 1.8 x A-m? Calculate the paramagnetic

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