Solid States

58. An excess of potassium ions makes KCl crystals appear violet or lilac in colour since ________. 

(i) Some of the anionic sites are occupied by an unpaired electron. 

(ii) Some of the anionic sites are occupied by a pair of electrons. 

(iii) There are vacancies at some anionic sites. 

(iv) F-centres are created which impart colour to the crystals. 

57. Which of the following statements are true about semiconductors? 

(i) Silicon doped with electron rich impurity is a p-type semiconductor. 

(ii) Silicon doped with an electron rich impurity is an n-type semiconductor. 

(iii) Delocalised electrons increase the conductivity of doped silicon. 

(iv) An electron vacancy increases the conductivity of n-type semiconductor. 

56. Under the influence of electric field, which of the following statements is true about the movement of electrons and holes in a p-type semiconductor? 

(i) Electron will move towards the positively charged plate through electron holes. 

(ii) Holes will appear to be moving towards the negatively charged plate. 

(iii) Both electrons and holes appear to move towards the positively charged plate. 

(iv) Movement of electrons is not related to the movement of holes. 

55. Which of the following statements are true about metals? 

(i) Valence band overlaps with conduction band. 

(ii) The gap between valence band and conduction band is negligible. 

(iii) The gap between valence band and conduction band cannot be determined. 

(iv) Valence band may remain partially filled. 

54. Which of the following statements are not true?

(i) Vacancy defect results in a decrease in the density of the substance. 

(ii) Interstitial defects results in an increase in the density of the substance. 

(iii) Impurity defect has no effect on the density of the substance. 

(iv) Frankel defect results in an increase in the density of the substance.

53. The value of magnetic moment is zero in the case of antiferromagnetic substances because the domains ________. 

(i) Get oriented in the direction of the applied magnetic field. 

(ii) Get oriented opposite to the direction of the applied magnetic field. 

(iii) Are oppositely oriented with respect to each other without the application of magnetic field. 

(iv) Cancel out each other’s magnetic moment. 

52. Which of the following is not true about the voids formed in 3-dimensional hexagonal close packed structure? 

(i) A tetrahedral void is formed when a sphere of the second layer is present above triangular void in the first layer. 

(ii) All the triangular voids are not covered by the spheres of the second layer. 

(iii) Tetrahedral voids are formed when the triangular voids in the second layer lie above the triangular voids in the first layer and the triangular shapes of these voids do not overlap. 

(iv) Octahedral voids are formed when the triangular voids in the second layer exactly overlap with similar voids in the first layer. 

51. Which of the following represents correct order of conductivity in solids? 

(i) κ metals >> κ insulators < κsemiconductors 

(ii) κmetals << κinsulators < κsemiconductors 

(iii) κmetals ? κsemiconductors > κinsulators = zero 

(iv) κ metals < κ semiconductors  > κinsulators  ≠  zero

50. The edge lengths of the unit cells in terms of the radius of spheres constituting fcc, bcc and simple cubic unit cell are respectively________. 

49. In the cubic close packing, the unit cell has ________. 

(i) 4 tetrahedral voids each of which is shared by four adjacent unit cells.

(ii) 4 tetrahedral voids within the unit cell. 

(iii) 8 tetrahedral voids each of the which is shared by four adjacent unit cells. 

(iv) 8 tetrahedral voids within the unit cells.