Note : Attempt four questions in all. Questions No. 1 and 2

Transcription

1 No. of Printed Pages : 8 I PHE-13 I BACHELOR OF SCIENCE (B.Sc.) Term-End Examination \ June, t4 PHYSICS PHE-13 : PHYSICS OF SOLIDS Time : 2 hours Maximum Marks : 50 Note : Attempt four questions in all. Questions No. 1 and 2 are compulsory. Symbols have their usual meaning. You may use log-table or non programmable calculator. 1. Answer any five parts : 5x3=15 Prove that for a close packed hcp lattice c \F8_ a 3 What are Miller indices? Discuss a scheme to determine the Miller indices of a plane. Explain ionic bonding and give two examples. The energy E of an electron in a crystalline solid is related to wave number k by the relation E k2 Calculate effective m mass and velocity of the electron. (e) Distinguish between piezoelectrics and pyroelectrics. PHE-13 1 P.T.O.

2 What is Meissner effect? How does it influence the perfect conductor model of a superconductor? What are liquid crystals? Discuss their technological importance. 2. Answer any three parts : 3x5=15 (a) List all possible symmetry operations in cubic crystals. Explain your statements. Draw all possible axis of rotational symmetry in a cube. For a simple cubic lattice with lattice constant a, calculate the distance between a family of (9, 5, 2) planes. Calculate the volume of the unit cell with the following basis vectors : a IA A) a (A A al = j + k ; a2 = k + i); 2 2 a r A) a3 = + j 2 Define mobility of a charge carrier. Obtain an expression for conductivity of an intrinsic semiconductor. How does it vary with temperature? Explain the term diamagnetism. Derive an expression for the susceptibility of a diamagnetic substance. PHE-13 2

3 Derive the dispersion relation for a linear diatomic 7+3 lattice. Explain the acoustic and optical modes of propagation in a diatomic crystal. OR State the assumptions of Debye model of lattice 2+8 heat capacity. Obtain an expression for heat capacity of a solid at low temperatures on the basis of Debye's models. Derive an expression for fermi energy of free 7+3 electrons in a crystalline solid for which the number of energy states in the energy range E and E + de is given by : Z(E)dE 8m L2 2 h2 3/2 EY2 de. The Fermi Energy of gold is 5.52 ev. Calculate the fraction of electrons excited above the Fermi level at room temperature. OR What is the optimum order of X-ray wavelengths 2+8 and energy to observe diffraction effects? Describe powder method for X-ray diffraction. Discuss formation of diffraction pattern on photographic film. 5. (a) What are nano-structures? List the 5 methods to obtain nano structures. Describe any one of them. PHE-13 3 P.T.O.

4 (b) How is thin film different from a bulk 5 material? Discuss the electrical and thermal properties of thin films. Physical Constants : kb =1.38 x10-23 JK-1. PHE-13 4

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6 4-11*(--R3rITT4 Errt? zff 371-d--4T-ew* -.nog, Hiso 311-1Trqff chttil t? -? 1 c 1 3t ft-47*i".ittii* 31(f : 3x5=15 Q,:t1 "Ef9174 cn.k.do Rift TN-4 ti i f---413# * ii+-111q I R* * TN-4'TM irti 3TV 311kfEiff I (i) IT-2411w a, cilc) on tit Amch 14 (9, 5, 2) * 3) 0 31Rid ' LlitchiCid (1 (.1 ct Tlf<VI a1c1 7** *rig*t 31-Prd9 rtch R1 cf.0 I a r IA A al = -2- j+k ; a 2 = 2 a k+i); a C:, a 3 = -2- airkw qffw 4 liclq11011 ITRITTrIfff *11 aitiqrff*- 'kv lictsboi re-r 04\31,4) 7:q ci 14 1i 11 "k 14.),H U ch1t 4itclrricl Si rci lei chcci 3TTIT fir Nor i t? s1 ra it m1 Tgiq TIV4-4743rd rc-k 04.14, vl PHE-13 6

7 3. Vff174 otiii uci tt ictt fcntfr#erurit4n-4--ayrru 7+3 I ra LW-Il uell q- 5I chlk1 ei 311-{ gaf fqtrr ti 4-1*11 I 3T2TaT IC1 c tllf(at ft0 1. 1T. 1fiT9FUTT 'q-dt R -crr mr-{ Via, -8)-P t ft4rt 4-1T(.1 da4-119frat 04\71ch 1;ITEr cr) I she v 1.> c.1 4 d),t,f 3TCF E 3t( E+dE 7+3 ala-mat -*-r ai m F figd t : 2 h2 3/2 E2 Z(E)dE - E y 2 de. alt.'to r4-409." -h4-11 dmit 044Ach I 411 4' evti o tcit d')'-r*rit 4 31n31C1 t*7k ai ry NR.Fro-r attrat fa ;NQ t rtfm ` *i f*-tuff -a-trr 2+8 i TrF 17. Ala lir? - f-n - f*-71 fafq t, ',1114)11 FLOC1-1 - fir SFr t-14 a1nit tip (a) qzif 11) W114 sill f i 5 faf fafirzil atir Trau-r*-11 PHE-13 7 P.T.O.

8 (b) ithoi tm2ft 1 i uct)r rim *? 5 fc5-0:11.1qo ath -gottm j auk sted-w eirtich : kb =1.38 x JK