125 + Interview Questions in Materials and Components in electronics and communication engineering Page 2 InterviewSolution

51.	The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100 cm/s respectively. The diffusion length of carriers is
Answer» Diffusion length = sqrt(Carrier life time x Diffusion constant) = (100 x 10-6 x 100)0.5 = 0.1 cm.

Discussion

52.	Yettrium-iron garnet (YFeO) is a soft magnetic material suitable for applications involving
Answer» Yettrium iron garnet has very low eddy current loss. Hence it is used at frequencies in MHz range.

Discussion

53.	If the number of atoms per unit volume of a monoatomic gas changes, the dielectric constant still remains constant.
Answer» The dielectric constant changes as it is proportional to the number of atoms per unit volume.

Discussion

54.	In a valence crystal, the valence electrons
Answer» In true valence crystals the binding between the atoms is accomplished by the sharing of valence electrons. This sharing can only be between neighbouring atoms only.

Discussion

55.	Automobile ignition systems use the principle of
Answer» A high voltage is induced due to mutual inductance because the number of turns in secondary coil is very high.

Discussion

56.	Electrical contact materials used in switches, brushes, relay must possess
Answer» Heat generated at contact should be dissipated quickly and contact should not melt.

Discussion

57.	The phenomenon of dielectric hysteresis occurs with
Answer» Hysteresis phenomenon occurs when direction of electric field is changed. This can happen only with ac.

Discussion

58.	If μ is permanent dipole moment and is absolute temperature, the orientation polarization of polyatomic gases is
Answer» Orientation polarization = Nμp2E/3 kT.

Discussion

59.	The charge per proton is
Answer» Because charge on proton is positive but numerically equal to that on electron.

Discussion

60.	Lines of magnetic field attract each other.
Answer» Lines of magnetic field repel each other.

Discussion

61.	As regards dielectric constant
Answer» εr is only a number and does not have any units.

Discussion

62.	A parallel plate capacitor having C = 200 x 10 F has loss dielectric having tan δ = 4 x 10. At an ac voltage of = 10 Hz and peak value 2 V, the dielectric losses are
Answer» Dielectric losses = v2 ωC tan δ.

Discussion

63.	The capacitance of a capacitor is not affected by
Answer» Capacitance depends on area, distance and ∈r but not on thickness of plates.

Discussion

64.	With increase in temperature, the electrical conductivity would
Answer» Increase in temperature causes resistivity of metals to increase and resistivity of intrinsic semiconductors to decrease. Conductivity is reciprocal of resistivity.

Discussion

65.	The resistance of a metallic wire would
Answer» As increases the resistance increases due to skin effect.

Discussion

66.	Nickel is a non-magnetic material.
Answer» Nickel is ferromagnetic material.

Discussion

67.	The dielectric losses do not depend on frequency.
Answer» Dielectric losses vary with frequency.

Discussion

68.	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
Answer» There are three principal quantum numbers.

Discussion

69.	For dielectrics in alternating field, polarizability is a complex quantity. The imaginary part of is zero for
Answer» Imaginary part of ae is zero for ω = 0 and ω = ∞.

Discussion

70.	In the wave mechanical theory, the maximum of the charge distribution in the ground state occurs for a distance from the nucleus equal to
Answer» The total charge associated with an electron moving about nucleus in the ground state of hydrogen atom is given by 4p2rr(r)dr. This integrand has a maximum value at r = radius of first Bohr orbit.

Discussion

71.	The number of valence electrons in pentavalent impurity is
Answer» Pentavalent means 5 valence electrons.

Discussion

72.	If the diameter of a wire is doubled, its current carrying capacity becomes
Answer» Current carrying capacity depends on area of cross-section.

Discussion

73.	The law J = σE, where J is current density, σ is electrical conductivity and E is field strength is
Answer» It is another form of Ohm's law.

Discussion

74.	A capacitor can be represented by a capacitance and resistance in parallel. For a good capacitor, this parallel resistance should be
Answer» The dielectric of a good capacitor should have very high resistivity.

Discussion

75.	As the viscosity of a liquid increases, the relaxation time
Answer» Relaxation time increases with viscosity.

Discussion

76.	The number of turns in a coil is doubled. If initial time constant is T, the new time constant is
Answer» When N is doubled, resistance becomes twice and inductance becomes four times. Since time constant is , time contant become twice.

Discussion

77.	The attraction between the nucleus and valence electron of copper atom is
Answer» The valence electron, in copper atom, can be easily detached from nucleus.

Discussion

78.	If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then
Answer» As the intrinsic carrier concentration is doubled, the concentration of both electrons and holes is doubled.

Discussion

79.	There is no hysteresis phenomenon is any dielectric material.
Answer» Hysteresis phenomenon exists in dielectic materials.

Discussion

80.	The units of μ and μ are
Answer» μr is only a numeric.

Discussion

81.	Which inductor is used at high frequencies?
Answer» Cast iron, sheet steel and iron alloy have very high hysteresis and eddy current losses at high frequencies.

Discussion

82.	For making a capacitor it is better to have a dielectric having
Answer» Capacitance is directly proportional to permittivity.

Discussion

83.	In solid insulator materials having only one kind of atom, the types of polarization which exist are
Answer» In elemental dielectrics only electronic polarization exists.

Discussion

84.	Antiferromagnetic materials do not have permanent dipoles.
Answer» Anti-ferromagnetic materials have permanent dispoles but antiparallel orientation of equal moments.

Discussion

85.	At room temperature, the current in intrinsic semiconductor is due to
Answer» Both electrons and holes contribute to flow of current in semiconductors.

Discussion

86.	Ferroelectric materials are those which
Answer» Ferroelectric materials have permanent polarization.

Discussion

87.	When temperature is above ferromagnetic Curie temperature, a ferromagnetic material
Answer» Above ferromagnetic Curie temperature, ferro-magnetic material behaves as a paramagnetic material.

Discussion

88.	A magnet does not attract
Answer» Only copper is non-magnetic.

Discussion

89.	For a paramagnetic material, susceptiblity increases with increasing temperature.
Answer» Susceptibility ∝ .

Discussion

90.	Hydrogen is used in
Answer» Modem large size generators have hydrogen cooling.

Discussion

91.	If is the charge of an electron, R is the radius of its orbit and ω is the angular velocity of electron, the magnetic dipole moment μ of the orbit is \|μ\| = ωR.
Answer» 1 μm 1 = 0.5 eωr2.

Discussion

92.	If ∈ and ∈ are the real and imaginary parts of complex dielectric constant ∈, and δ is the loss angle. Then
Answer» If ∈r" = 0, δ = 0.

Discussion

93.	An air cored inductance is a
Answer» Because of air core, inductance is constant.

Discussion

94.	A vacuum parallel plate capacitor is charged. The field between the plates is 2 x 10 V/m. If the space between the plates is filled with a material having ∈ = 10, then the value of field in the dielectric will be
Answer» D ∝ ∈rE. The flux density is the same. Since ∈r has become 10 times, E decreases by 10 times.

Discussion

95.	Which inductor is linear?
Answer» For magnetic materials, permeability is not constant.

Discussion

96.	In metals the valence electron wave functions are strongly perturbed by the presence of neighbouring atoms.
Answer» In a metal valence electrons are shared by all atoms.

Discussion

97.	The units of polarization of dielectric are
Answer» Polarization P = ∈0(∈r - 1)E. Therefore units of Polarization = .

Discussion

98.	When a potential is applied across an intrinsic semiconductor, holes flow
Answer» Holes are positively charged and move away from positive terminal.

Discussion

99.	Which element exhibits the property of inertia?
Answer» Inductance opposes rise and decay of current. Hence it has the property of inertia.

Discussion

100.	For a permanent magnetic material
Answer» Materials suitable for permanent magnet have large hysteresis loop. Hence residual and coercive field are large.

Discussion

Explore topic-wise InterviewSolutions in .

The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100 cm/s respectively. The diffusion length of carriers is

Yettrium-iron garnet (YFeO) is a soft magnetic material suitable for applications involving

If the number of atoms per unit volume of a monoatomic gas changes, the dielectric constant still remains constant.

In a valence crystal, the valence electrons

Automobile ignition systems use the principle of

Electrical contact materials used in switches, brushes, relay must possess

The phenomenon of dielectric hysteresis occurs with

If μ is permanent dipole moment and is absolute temperature, the orientation polarization of polyatomic gases is

The charge per proton is

Lines of magnetic field attract each other.

As regards dielectric constant

A parallel plate capacitor having C = 200 x 10 F has loss dielectric having tan δ = 4 x 10. At an ac voltage of = 10 Hz and peak value 2 V, the dielectric losses are

The capacitance of a capacitor is not affected by

With increase in temperature, the electrical conductivity would

The resistance of a metallic wire would

Nickel is a non-magnetic material.

The dielectric losses do not depend on frequency.

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

For dielectrics in alternating field, polarizability is a complex quantity. The imaginary part of is zero for

In the wave mechanical theory, the maximum of the charge distribution in the ground state occurs for a distance from the nucleus equal to

The number of valence electrons in pentavalent impurity is

If the diameter of a wire is doubled, its current carrying capacity becomes

The law J = σE, where J is current density, σ is electrical conductivity and E is field strength is

A capacitor can be represented by a capacitance and resistance in parallel. For a good capacitor, this parallel resistance should be

As the viscosity of a liquid increases, the relaxation time

The number of turns in a coil is doubled. If initial time constant is T, the new time constant is

The attraction between the nucleus and valence electron of copper atom is

If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then

There is no hysteresis phenomenon is any dielectric material.

The units of μ and μ are

Which inductor is used at high frequencies?

For making a capacitor it is better to have a dielectric having

In solid insulator materials having only one kind of atom, the types of polarization which exist are

Antiferromagnetic materials do not have permanent dipoles.

At room temperature, the current in intrinsic semiconductor is due to

Ferroelectric materials are those which

When temperature is above ferromagnetic Curie temperature, a ferromagnetic material

A magnet does not attract

For a paramagnetic material, susceptiblity increases with increasing temperature.

Hydrogen is used in

If is the charge of an electron, R is the radius of its orbit and ω is the angular velocity of electron, the magnetic dipole moment μ of the orbit is |μ| = ωR.

If ∈ and ∈ are the real and imaginary parts of complex dielectric constant ∈, and δ is the loss angle. Then

An air cored inductance is a

A vacuum parallel plate capacitor is charged. The field between the plates is 2 x 10 V/m. If the space between the plates is filled with a material having ∈ = 10, then the value of field in the dielectric will be

Which inductor is linear?

In metals the valence electron wave functions are strongly perturbed by the presence of neighbouring atoms.

The units of polarization of dielectric are

When a potential is applied across an intrinsic semiconductor, holes flow

Which element exhibits the property of inertia?

For a permanent magnetic material