Materials and Components Questions

• Magnetic phase above Curie temperature When the temperature of a ferromagnetic material exceeds its Curie temperature, what magnetic behavior does it exhibit?
• RL time constant change when the number of turns is doubled A coil in an RL circuit is rewound so that the number of turns is doubled, with similar wire and form factor so that resistance scales roughly with length. If the initial time constant is T, what is the new time constant?
• Is relative permittivity (εr) set by atomic structure? Decide whether the statement is correct: “The relative permittivity εr of a dielectric is determined by the material’s atomic and molecular structure (i.e., its available polarization mechanisms).”
• Allowed principal quantum numbers for the hydrogen atom When solving the time-independent Schrödinger equation for an electron in the Coulomb field of a proton (hydrogen atom), which statement about the principal quantum number n yields physically acceptable bound-state wavefunctions?
• Constitutive relation in magnetized media (SI units) Let B denote magnetic flux density (tesla), H the magnetic field intensity (A/m), and M the magnetization (A/m). Assess the validity of the statement: B = μ0 * (H + M).
• Assertion–Reason on amorphous solids formation Assertion (A): An amorphous material is obtained when atomic mobility is strongly inhibited during solidification (e.g., rapid quenching). Reason (R): For most solids, the crystalline state is the natural equilibrium state.
• Linearity of an air-cored inductor at fixed frequency Consider an ideal air-cored inductor operated at a fixed frequency with sinusoidal excitation. How should it be classified regarding linearity, and why?
• Valence electrons of a trivalent impurity (semiconductor doping) In semiconductor terminology, a “trivalent impurity” has how many valence electrons?
• Assertion–Reason on conductor response Assertion (A): In a homogeneous conductor, the current density J remains constant in time as long as the applied electric field E is constant. Reason (R): Ohm’s law in point form states J = σE (with σ constant for the given state).
• Primary interatomic attraction responsible for the formation of solids Which fundamental interaction most directly accounts for the cohesive forces (chemical bonding) that form and hold solids together?
• Units of polarization P in SI (dipole moment per unit volume) Select the correct SI unit for dielectric polarization P (defined as electric dipole moment per unit volume).
• Antiferromagnetism and permanent moments — true or false? “Antiferromagnetic materials do not possess permanent magnetic dipole moments.”
• Periodic table position of silicon and germanium (group classification) Silicon (Si) and germanium (Ge) belong to which column (group) of the periodic table?
• Energy of an induced dipole in a uniform electric field An atom with electric polarizability a is placed in a homogeneous electric field E. What is the energy stored in (or magnitude of the lowering of) the polarized atom due to the induced dipole?
• Capacitor equivalent circuit – leakage resistance (parallel R) requirement A practical capacitor is often represented by an ideal capacitance in parallel with a resistance that models insulation/leakage. For a good-quality capacitor used in electronics and power systems, this parallel resistance should be:
• Carrier motion in an intrinsic semiconductor under applied voltage When a potential difference is applied across a pure (intrinsic) semiconductor, in which direction do the positively charged 'holes' drift inside the semiconductor body?
• Vacuum permittivity epsilon_0 (ε0): physical meaning beyond unit conversion The statement 'ε0 has no other physical meaning than that of a fundamental conversion factor' is:
• Basics of n-type semiconductors – charge neutrality and doping examples Which statement correctly describes n-type semiconductors and their formation by impurity addition?
• Assertion–Reason on acceptor (p-type) semiconductors and conductivity Assertion (A): An acceptor-doped (p-type) extrinsic semiconductor has higher conductivity than the intrinsic semiconductor at the same temperature. Reason (R): Adding a p-type impurity introduces an allowable discrete acceptor energy level just above the valence band, enabling easier hole formation.
• Ground-state hydrogen in wave mechanics – most probable electron–nucleus separation In the quantum (wave-mechanical) description of hydrogen, the radial probability density for the ground state (1s) is maximum at a separation equal to which Bohr radius?