51. In a piezoelectric crystal, the application of mechanical force will cause
52. Consider the following statement
If an electric field is applied to an n type semiconductor bar, the electrons and holes move in opposite directions due to their opposite charges. The net currents is both due to electrons and holes with electrons as majority carrierssum of hole and electron currentsdifference between electron and hole currents. Which of above statements are correct?
53. As the temperature of a pure silicon specimen is increased
54. Assertion (A): In many materials, dielectric polarization causes mechanical distortion.Reason (R): If dielectric polarization causes mechanical distortion then mechanical distortion must cause dielectric polarization.
55. Semi conducting materials are all
56. Silicon and germanium atoms combine orderly into array of atoms located in repetitive geometric pattern. This pattern is called
57. In a pure sample of silicon
58. Orbital magnetic dipole moment is due to the motion of electron in its orbit around nucleus.
59. Assertion (A): ∈r can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.Reason (R): Capacitance of a parallel plate capacitor = .
60. In a homogeneous magnetic field H of a solenoid, the core carries a magnetic dipole moment M per unit volume equal to
61. The field pattern of a solenoid is similar to that of bar magnet.
62. Assertion (A): In a parallel plate capacitor having area of plate 1 m2 and plate separation 1 m, the capacitance C and resistance R are given by C = ∈0∈'r and R = where ω is frequency, ∈r' and ∈r" are real and imaginary parts of dielectric constant.Reason (R): The imaginary part of electric constant is responsible for dielectric losses.
63. Assertion (A): Silicon is the most favoured semiconductor material.Reason (R): PIV for silicon diode is more than that for germanium diode.
64. Assertion (A): When cathode temperature is increased from 2500 K to 2550 K, thermionic emission current may increase by about 50%.Reason (R): Thermionic emission current ∝ T2 e-Ew/kT.
65. In molecules of ionic crystals, orientation polarization is zero.
66. Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment.Reason (R): The structure of CO2 is O = C = O.
67. For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in
68. A permeable substance is one
69. When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ∈'r - j∈"r . In such materials, the dielectric losses under alternating stress is proportional
70. The classes of solid dielectrics are
71. A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be
72. A material which is lightly repelled by a magnetic field is known as
73. Which of the following is the poorest conductor of electricity?
74. The magnetic moment in units of Bohr magneton of a ferrous ion in any ferrite is
75. The relationship of hysteresis loss to maximum flux density was first determined by