76. In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as
77. Assertion (A): If WF is Fermi energy, v is velocity of electron and m is mass of electron, then .Reason (R): Conductivity of a metal depends on temperature and impurity concentration.
78. Dielectric constant of transformer oil is about
79. Assertion (A): When an electron is revolving in its orbit and magnetic field is also present, the angular frequency of electron will be affected by the magnetic field.Reason (R): In the case of electron revolving in its orbit in the presence of magnetic field, the orbital magnetic dipole moment is not affected by the presence of magnetic field.
80. In carbon resistor colour code, the third band is red. It indicates
81. Rochelle salt is a ferroelectric material.
82. Paramagnetic materials have permanent magnetic dipoles but interaction between neighbouring dipoles is negligible.
83. Assertion (A): If difference between static and optical dielectric constant is high, the mechanical compressiblity of that material is also high.Reason (R): For soft ions, ionic polarization per unit field is higher than that of hard ions.
84. Assertion (A): In Figure, the intercept of the line on y-axis is equal to N (a e + a i), where N is number of atoms/m3, a e is electronic polarizability and a i is ionic polarizability.Reason (R): a e and a i are independent of temperature.
85. Assertion (A): The optical dielectric constant (i.e., εr at optical frequencies)of ionic dielectrics is less than static dielectric constant. Reason (R): At optical frequencies, Pi = 0.
86. A piece of iron is placed in a magnetic field
87. Assertion (A): Magnetism can be explained by the theory of magnetic domains.Reason (R): The existence of magnetic domains is evident from the Bitter powder patterns.
88. Ferromagnetic materials
89. In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will
90. Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic.Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions t c are related as λ = vTc.
91. Assertion (A): Copper is a monoatomic solid.Reason (R): In a metal the valence electrons belong to all atoms.
92. The heat developed per m3 per second (W) in a conductor having a conductivity σ and a field E is
93. The number of valence electrons in acceptor impurity are
94. If q is charge on an electron, R is radius of electron orbit and ω is angular velocity of electron rotation, the magnetic dipole moment of electron in orbit is
95. At a very low temperature, a semiconductor
96. The colour code on a carbon resistor is red-red-black-silver. The value of resistor is
97. Some typical examples of macroscopic quantities are
98. The temperature coefficient of a thermistor
99. Assertion (A): Helium, Argon and Neon are gaseous at room temperature.Reason (R): The atoms in Helium, Argon and Neon are chemically extremely inactive.