Materials and Components Questions

• Classical bound-charge model – polarizability of a harmonically bound charge A particle of charge Q (coulombs) is elastically bound to its equilibrium position with spring constant f (newtons per metre). Under a static electric field E, what is the polarizability α of this one-particle system?
• Bohr model stability condition for hydrogen In a hydrogen atom, an electron orbits a proton. According to the Bohr (classical) picture, orbital stability requires equilibrium between the attractive Coulomb force and the required centripetal force. Is this statement correct?
• Maximum number of electrons in an electron shell (principal quantum number n) For a given principal quantum number n, what is the maximum number of electrons that can occupy that shell?
• Dielectric losses and loss tangent (tan δ) Assertion (A): Dielectric power losses are proportional to tan δ (the loss tangent) for a given frequency, field, and permittivity. Reason (R): The loss tangent is defined by tan δ = εr'' / εr', where εr' and εr' denote the real and imaginary parts of the complex relative permittivity εr.
• Ferroelectrics – spontaneous polarization State whether the following is correct: “Spontaneous polarization (a remanent electric dipole alignment without external field) occurs in ferroelectric materials.”
• Magnetostatics: Expressing magnetic flux density B in terms of field strength H, magnetization M, and the vacuum permeability μ0 For a magnetic core characterized by relative permeability μr, magnetization (magnetic dipole moment per unit volume) M, and applied magnetic field strength H, which general SI relationship gives the flux density B?
• Temperature dependence of relative permittivity: role of permanent dipoles Assertion (A): In some materials, the relative permittivity εr is essentially independent of temperature, while in others εr varies with temperature. Reason (R): If permanent dipoles are absent, εr varies with temperature.
• Direction of force on a current-carrying conductor in a magnetic field Which rule should be used to determine the direction of the mechanical force on a straight conductor carrying current when placed in a magnetic field?
• Dielectric loss and complex permittivity at low frequency A dielectric has ε′ = 2.1 and loss tangent tanδ = 5 × 10^-4 at 100 Hz. What is the imaginary part of its complex relative permittivity ε″ at 100 Hz?
• Inductance scaling with number of turns for a fixed-geometry single-layer air-core coil A single-layer air-core coil has n turns and inductance L. If a new coil is wound with 2n turns while keeping length and diameter the same, what is the new inductance?
• Magnetic ordering: identifying the characteristic temperature in antiferromagnets In antiferromagnetic materials, the plot of magnetic susceptibility versus temperature exhibits a sharp maximum at a specific temperature. What is this temperature called?
• Electronic polarization in rare gases: nucleus shift under an external field When a rare-gas atom is placed in a uniform electric field, the positively charged nucleus shifts slightly relative to the center of its electron cloud by a distance x. If R is the approximate radius of the electron cloud, which relation best describes x compared to R?
• Units of electric dipole moment in SI What are the correct SI units for electric dipole moment p?
• Magnetic response of superconductors (Meissner effect) For an ideal superconductor in its superconducting state, what is the effective relative permeability μr inside the material?
• Electrical conductivity of copper — assertion–reason Assertion (A): Copper is a good conductor of electricity. Reason (R): Copper has a face-centred cubic (FCC) crystal lattice.
• Photon energy and band gap from laser wavelength — GaAs laser at 867 nm A GaAs laser emits light of wavelength 8670 × 10^−10 m. Given h = 6.626 × 10^−34 J·s, c = 3 × 10^8 m/s, and 1 eV = 1.602 × 10^−19 J, the energy gap (in eV) of GaAs is:
• Permittivity concepts — assertion–reason Assertion (A): Relative permittivity εr of a material is determined by its atomic and molecular structure. Reason (R): Absolute permittivity ε0 is determined by the atomic structure of the material.
• Atomic structure — what forms the core of an atom? Select the most accurate description of the atom's core:
• Diamagnetism and permanent dipoles — true or false? “Diamagnetic materials do not possess permanent magnetic dipoles.”
• Assertion–Reason: Rochelle salt and BaTiO3 as ferroelectrics Assertion (A): Rochelle salt and barium titanate are ferroelectric materials. Reason (R): Ferroelectric materials exhibit hysteresis in their polarization–electric field (P–E) characteristics.