Materials and Components Questions

• A good dielectric should have
• The temperature coefficient of resistivity of semiconductors is
• Which of these has the highest dielectric strength?
• When a dielectric is subjected to an electric field E, each volume element of dielectric can be considered to be carrying an electric dipole moment.
• Assertion (A): Doping level in extrinsic semiconductors is very small. Reason (R): Additional of impurity in the ratio of 1 part in 108 parts increases the number of charge carriers by about 20.
• Which of the following is used in automatic control of street lights?
• A leaky dielectric has ∈r = ∈r' - j∈r". If a field E is applied, the current component in phase with E is proportional to ∈r".
• The colour code on a carbon resistor is yellow-violet-orange. The value of resistance is
• An electron in a metal suffers collision and if the probability of it being scattered over an angle dθ is 2p P(θ) sin θ dθ where P(θ) is an arbitrary function of scattering angle θ, then
• The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is
• Assertion (A): Ionic solids, in general, have no electrical conductivity. Reason (R): In ionic solids, electrons are tightly bound to the nucleus.
• In which of the following semiconductor are holes minority carriers
• The number of valence electrons in silicon atom is
• When temperature is above ferromagnetic Curie temperature, a ferromagnetic material
• The number of turns in a coil is doubled. If initial time constant is T, the new time constant is
• ∈r is determined by the atomic structure of the dielectric.
• When Schrodinger equation is applied to the motion of electron in the field of protons, the physically acceptable solutions for the wave function exist for quantum number which are
• If B, H and M denote flux density, field intensity and magnetisation, B = μ0 (H + M).
• Assertion (A): An amorphous material is obtained when mobility of atoms is inhibited during solidification. Reason (R): Crystalline state is a natural state for most solids.
• An air cored inductance is a