Materials and Components Questions

• Which circuit element exhibits electrical “inertia,” i.e., opposition to changes in current rather than to the current itself?
• True/False (Bonding): In a purely covalent (valence) crystal, the bonding between atoms is accomplished by sharing valence electrons.
• Units check: What are the units of the permeability of free space μ₀ and the relative permeability μ_r?
• Assertion–Reason (Fermi–Dirac statistics): At any nonzero temperature, the probability that an energy state E equal to the Fermi level E_F is occupied equals 0.5. Reason: The Fermi–Dirac function f(E) = 1 / (1 + exp[(E − E_F) / (kT)]) gives f(E_F) = 1 / (1 + exp(0)) = 0.5.
• If two resistive materials with temperature coefficients of resistance 0.004 and 0.0004 per °C are connected in series, what is the overall temperature coefficient for the series combination?
• If the diameter of a circular wire is doubled while using the same permissible current density, its current-carrying capacity becomes what multiple of the original value?
• Intrinsic semiconductor behavior — effect of temperature on carriers in pure silicon As the temperature of a pure (intrinsic) silicon specimen increases, what happens to the concentrations of free electrons and holes?
• Onset of superconductivity — electrical resistivity outcome When a material transitions into the superconducting state (below its critical temperature), its electrical resistivity becomes:
• Wiedemann–Franz law in metals In metals, the thermal conductivity K and electrical conductivity σ satisfy K/(σ T) = L. The constant L is called the:
• Carrier transport — definition of mobility In metals (and more generally in conductors/semiconductors), the average electron drift velocity per unit electric field is called mobility. True or false?
• Crystalline arrangement in elemental semiconductors Silicon and germanium atoms join in an orderly, repeating arrangement of atoms in three dimensions. This repeating geometric pattern is called a:
• Transformer insulating oil — typical dielectric constant (relative permittivity) The dielectric constant (relative permittivity) of mineral transformer oil is approximately:
• Carbon resistor colour code — meaning of the third band (multiplier) In the standard 4-band colour code for carbon resistors, the third band is red. What does this indicate?
• Materials science and dielectrics — assertion–reason on electro-mechanical coupling Assertion (A): In many dielectric materials, applying an electric field (and thus producing dielectric polarization) can cause mechanical distortion of the solid. Reason (R): If dielectric polarization causes mechanical distortion, then the converse must always hold; namely, any mechanical distortion will necessarily cause dielectric polarization in that material.
• Semiconductor physics — current components in an n-type bar under an electric field Consider an n-type semiconductor bar placed in an applied electric field. Electrons and holes drift in opposite directions because of their opposite charges. Evaluate the following statements: 1) The net current is contributed by both electrons and holes, with electrons as the majority carriers. 2) The net current equals the sum of the electron and hole current components. 3) The net current equals the difference between the electron and hole currents. Which statements are correct?
• Dielectrics — determining relative permittivity from capacitor measurements (assertion–reason) Assertion (A): The relative permittivity εr of a dielectric can be found experimentally by measuring the capacitance of a parallel-plate capacitor with and without the dielectric inserted. Reason (R): For a parallel-plate capacitor, the capacitance is C = ε A / d = ε0 εr A / d, where A is plate area and d is plate spacing.
• Ferrites and ionic moments — magnetic moment of a ferrous (Fe2+) ion in ferrites What is the magnetic moment, expressed in Bohr magnetons (μB), typically attributed to a ferrous ion (Fe2+) within ferrite materials under the spin-only approximation?
• Dielectrics at optical frequencies — assertion–reason on εr and ionic polarization Assertion (A): For ionic dielectrics, the optical dielectric constant (εr measured at optical frequencies) is less than the static dielectric constant. Reason (R): At optical frequencies, the ionic polarization component Pi is effectively zero (only electronic polarization responds).
• Magnetization in a solenoid core — relation between M and H in SI units In a uniform magnetic field H inside a solenoid, the magnetized core has magnetization (dipole moment per unit volume) M equal to which expression?
• Polarization mechanisms — ionic crystals and orientation polarization State whether the following is true or false: “In molecules of ionic crystals, the orientation polarization component is zero.”