Materials and Components Questions

• In a metal, the drift velocity of electrons in the presence of a electric field E is
• Inductors used at V.H.F. are made using
• Assertion (A): The resistance of a copper specimen changes by about 22% when temperature is increased from room temperature to 700°C. Reason (R): The physical properties of a material are determined mostly by the extent of impurities.
• Assertion (A): For elemental dielectrics, P = NaeEi where N is number of atoms/m3, P is polarization, ae is electronic polarization and Ei is internal electric field. Reason (R): In elemental dielectrics there are no permanent dipoles or ions.
• The dielectric constant of ferroelectric materials can be expressed by the equation
• If a capacitor C having selectivity factor Q is scaled down in all its dimensions by a factor K without any altering the dielectric material, the new capacitor will have capacitance and selectivity as
• Which solid dielectric has highest temperature limit?
• Assertion (A): An electron having charge - e and mass m and lying in an electric field E is subjected to an acceleration - (e/m) E. Reason (R): If there are n electrons/m3 moving with velocity vx and each electron has a charge - e, the current density J = - n evx.
• Assertion (A): Orbital magnetic moment of an electron in an atom is of the order of 1 Bohr magneton. Reason (R): 1 Bohr magneton = 9.27 x 10-24 A/m2.
• When a pentavalent impurity is added, the semiconductor becomes
• For a polyatomic gas, the equation relating dielectric constant ∈r with molecular properties is
• Assertion (A): For most metals, Fermi energy EF is less than 10 eV. Reason (R): Fermi level of a metal is given by EF = 3.64 x 10-19 (n)2/3 where n is number of free electrons/m3 of metal.
• The relaxation time of electrons in a metal is of the order of
• As regards ∈0 and ∈r (absolute and relative permittivity)
• An electron is moving in a circular orbit of radius R at angular velocity ω0 in a field free space. If a magnetic field B is created, the velocity of electron ω will be given by the equation
• Even at room temperature, an intrinsic semiconductor has some holes. These holes are due to
• At a very low temperature, a semiconductor
• Assertion (A): Helium, Argon and Neon are gaseous at room temperature. Reason (R): The atoms in Helium, Argon and Neon are chemically extremely inactive.
• The colour code on a carbon resistor is green-blue-yellow. The tolerance is
• The transition of electron from energy level W1 to W2 is associated with emission or absorption of electro magnetic radiation of frequency f such that