Tiêu đề 26. SEMI CONDUCTORS and ELECTRONIC DEVICES EASY Ans.pdf ✅

1. (d) Ionic bonds cone into being when atoms that have low ionization energies, and hence lose electrons rapidly, interact with other atoms that and to acquire excess electrons. The former atoms give up electrons to the latter and they there upon become positive and negative ions respectively. 2. (d) For tetragonal, cubic and orthorhombic system  =  =  = 90  . 3. (d) Tourmaline crystal is biaxial. 4. (a) The temperature co-efficient of resistance of conductor is positive. 5. (a) Density 3 N(a) nA  = where n = 2 for bcc structure , A = 39  10–3 kg, N = 6.02  1023 , a d (4.525 10 )m 3 2 3 2 −10 = =   (d = nearest neighbour distance = distance between centres of two neighbouring atoms 2 a = ) On putting the values we get  = 907 6. (a) The highest energy level which an electron can occupy in the valence band at 0 K, is called Fermi energy level. 7. (a) In a triclinic crystal a  b  c and       90° 8. (b) Metallic solids are opaque because incident light is absorbed by the free electrons in a metal. 9. (a) In ionic bonding electrons are transferred from one type of atoms to the other type creating positive and negative ions. For example in NaCl, Na loses one electrons and Cl gains one so that Na+ and Cl– ions have a stable shell structure. 10. (c) Wood is non-crystalline. 11. (d) Cu has fcc structure, for fcc structure co-ordination number = 12 12. (c) Vander Waal force is weak dipole-dipole interaction. 13. (b) 14. (a) The sodium chloride crystal structure has a fcc lattice with one chloride ion at each lattice point and one sodium ion half a cube length above it. 15. (a) In NaCl crystal Na+ ion is surrounded by − 6 Cl ion, therefore coordination number of Na+ is 6. 16. (a) Sodium has bcc structure. The distance between body centre and a corner 2 3 a = 3.66 Å 2 3 4.225 =  = 17. (d) 18. (b) For the fcc structure 2 2 1 / 2 4r = (a + a ) = a 2  4 2 2 a 2 a r = = 19. (c) Metals reflects incident light by the vibrations of free electrons under the influence of electric field of incident wave. The conductivity of metals decreases with increase of temperature due to increase in random motion of free electrons. The bonding is therefore metallic. 20. (c) 21. (b) The nearest distance between two atoms in a bcc lattice = 2 (atomic radius) 2 3 4 3 2 a a =         =  22. (a) The net force on electron placed at the centre of bcc structure is zero. (By the principle of superposition of couloumb forces) 23. (b) For bcc packing, distance between two nearest atoms         = = 4 3 2 2 a d r  Lattice constant Å d a 4.3 3 2 3.7 3 2 =  = = 24. (a) 25. (d) 2 a = 4r  r Å r a 2(2 ) 2 2.54 3.59 2 4 = = =  = 26. (d) 27. (d) Covalent bonding exists in semi-conductor. 28. (d) In H2O covalent bonding is present. a a a r r r r a a
29. (c) In P-type semiconductors, holes are the majority charge carriers 30. (b) Ga has a valancy of 3. 31. (b) Since ne > nh; the semiconductor is N-type. 32. (b) Absence of one electron, creates the positive charge of magnitude equal to that of electronic charge. 33. (b) Ge + impurity Pantavalen t semiconductor N - type 34. (b) Impurity increases the conductivity. 35. (c) semiconductor Intrinsic Conductivity is due to the breaking of covalent bond semiconductor Extrisnsic Conductivity is due to the breaking of covalent bond and excess of charge carriers due to impurity. 36. (d) Resistance of conductors (Cu) decreases with decrease in temperature while that of semi-conductors (Ge) increases with decrease in temperature. 37. (a) Aluminum is trivalent impurity. 38. (b) With temperature rise conductivity of semiconductors increases. 39. (a) 40. (a) 41. (d) In insulators, the forbidden energy gap is largest and it is of the order of 6 eV. 42. (c) N-type semiconductors are neutral because neutral atoms are added during doping. 43. (b) 44. (b) In insulators, the forbidden energy gap is very large, in case of semiconductor it is moderate and in conductors the energy gap is zero. 45. (b) 46. (c) Phosphorus is pentavalent. 47. (c) In intrinsic semiconductors, the creation or liberation of one free electron by the thermal energy has created one hole. Thus in intrinsic semiconductors ne = nh 48. (d) Conductor has positive temperature coefficient of resistance but semiconductor has negative temperature coefficient of resistance. 49. (b) Boron is trivalent. 50. (a, c) In intrinsic semiconductors, electrons and holes both are charge carriers. In P-type semiconductors (Extrinsic semiconductors) holes are majority charge carriers. 51. (d) 52. (b) 53. (c) Eg(Germanium ) = 0.67 eV 54. (d) In P-type semiconductors, holes are majority charge carrier and electrons are minority charge carriers. 55. (c) At zero Kelvin, there is no thermal agitation and therefore no electrons from valence band are able to shift to conduction band. 56. (c) Antimony is a fifth group impurity and is therefore a donor of electrons. 57. (b) Resistance of semiconductor Temperatur e 1  58. (d) S.C. Extrinsic Type ( ) Type ( ) e p p e N n n P n n −  −  59. (a) At room temperature the number of electrons and holes are equal in the intrinsic semiconductor. 60. (b) Indium is trivalent, hence on doping with it, the intrinsic semiconductor becomes P-type semiconductor. 61. (a) V.B. C.B. Ef Energy gap (Eg)
62. (c) In semiconductors, Forbidden energy gap is of the order of 1 eV. 63. (d) At 0K temperature semiconductor behaves as an insulator, because at very low temperature electrons cannot jump from the valence band to conduction band. 64. (c) Antimony is pentavalent. 65. (b) At 0K semiconductor behaves as insulator so it's resistance is infinite. 66. (d) The conduction and valence bands in the conductors merge into each other. 67. (a) For N-type semiconductor, the impurity should be pentavalent. 68. (d) When a free electron is produced, simultaneously a hole is also produced. 69. (c) For P − type semiconductor the doping impurity should be trivalent. 70. (b) The temperature co-efficient of resistance of a semiconductor is always negative. 71. (c) The resistance of semiconductor decreases with the increase in temperature. 72. (d) At absolute zero temperature, semiconductor. 73. (b) Formation of energy bands in solids are due to Pauli's exclusion principle. 74. (a) In P-type semiconductors, holes are majority charge carriers. 75. (b) 76. (a) Conductivity of semiconductors increases with rise in temperature. 77. (d) All are trivalent in nature. 78. (d) In N-type semiconductors, electrons are majority charge corners. 79. (b) When a strong current passes through the semiconductor it heats up the crystal and covalent bond are broken. Hence because of excess number of free electrons it behaves like a conductor. 80. (b) 81. (a) Phosphorus is a pentavalent impurity so ne > nh. 82. (c) Phosphorus is pentavalent while Indium is trivalent. 83. (d) Phosphorus and Arsenic both are pentavalent. 84. (b) 85. (d) 86. (a) For Ge, E eV J J g 19 19 0.7 0.7 1.6 10 1.12 10 − − = =   =  87. (a) At room temperature some covalent bond breaks and semiconductor behaves slightly as a conductor. 88. (b) 89. (a) 90. (c) Because boron is a trivalent impurity. 91. (a) In P-type semi conductor, holes are majority charge carriers. 92. (b) In intrinsic semiconductors, at room temperature ne = nh. 93. (a) In conductors valence band and conduction band overlaps. 94. (c) Because As is pentavalent impurity. 95. (c) At 0 K semiconductor behaves as an insulator. 96. (c) 97. (c) 98. (b) Antimony and phosphorous both are pentavalent. 99. (b) Gallium is trivalent impurity. 100. (a) 101.(b) One atom of pentavalent impurity, donates one electron. 102. (c) 103.(b) The charge on hole is positive. 104.(c) Phosphorus is pentavalent impurity.
105. (a) ni = nhne 2  = ne 19 2 21 (10 ) 10  10 / . 17 3 ne = m 106.(d) Temperature co-efficient of semiconductor is negative. 107.(a) Copper, Aluminum, Iron are conductors, while Ge is semiconductor. 108.(a) At room temperature, few bonds breaks and electron hole pair generates inside the semiconductor. 109. (a) 110.(b) With rise in temperature, conductivity of semiconductor increases while resistance decreases. 111.(d) Gallium, boron and aluminum are trivalent. 112.(c) Because with rise in temperature, resistance of semiconductor decreases, hence overall resistance of the circuit increases, which in turn increases the current in the circuit. 113. (d) Extrinsic semiconductor (N-type or P-type) are neutral. 114.(a) Because n eA i v e d ( ) = 115. (c) 116. (b) Resistivity is the intrinsic property, it doesn't depend upon length and shape of the semiconductors. 117. (c) 118. (a) Å E hc 10888 1.14 1.6 10 6.6 10 3 10 19 34 8 max =      = = − −  119.(b) In N-type semiconductor impurity energy level lies just below the conduction band. 120. (d) 121. (d) 122.(d) e e  = en   16 3 19 3900 10 / 1.6 10 6.24 cm e n e e =  = = −    123. (d) In semiconductors, the forbidden energy gap between the valence band and conduction band is very small, almost equal to kT. Moreover, valence band is completely filled where as conduction band is empty. 124.(d) In sample x no impurity level seen, so it is undoped. In sample y impurity energy level lies below the conduction bond so it is doped with fifth group impurity. In sample z, impurity energy level lies above the valence band so it is doped with third group impurity. 125.(a) Forbidden energy gap for carbon is greater than that of silicon. 126. (b) 127. (a) Because electrons needed less energy to move. 128. (b) 129. (b) 130.(a) In forward biased PN-junction, external voltage decreases the potential barrier, so current is maximum. While in reversed biased PN-junction, external voltage increases the potential barrier, so the current is very small. 131. (b) 132.(b) Filter circuits are used to get smooth dc  -filter is the best filter. 133.(c) In reverse bias no current flows. 134.(b) In reverse biasing, width of depletion layer increases. 135.(a) Depletion layer consist of mainly stationary ions. 136.(b) Current flow is possible and A R V i 2 10 300 (4 1) − = − = = 137.(a) The potential of P-side is more negative that of N-side, hence diode is in reverse biasing. In reverse biasing it acts as open circuit, hence no current flows. 138. (a) 139.(b) It is used to convert ac into dc (rectifier) P N + –