595 + Mcqs in Materials And Components Page 2 McqOptions

51.	For a polyatomic gas, the equation relating dielectric constant ∈r with molecular properties is
A.	[A].
B.	[B].
C.	[C].
D.	[D].
Answer» B. [B].

Discussion

52.	A dielectric of relative permittivity ∈r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by
A.	P = constant
B.	P = ∈0 E
C.	P = ∈0(∈r - 1) E
D.	P = ∈r E
Answer» D. P = ∈r E

Discussion

53.	An iron specimen has µr = 1000 when B = 0.3 T. If B = 0.35 T, µr
A.	will be 1000
B.	will be less than 1000
C.	will be more than 1000
D.	may be more or less than 1000
Answer» E.

Discussion

54.	In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will
A.	increase
B.	decrease
C.	first decrease then increase
D.	first increase then decrease
Answer» E.

Discussion

55.	Hall effect is observed in a specimen (metal or semi conductor) when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is
A.	ormal to both current and magnetic field
B.	n the same direction as current
C.	n a direction anti parallel to magnetic field
D.	one of the above
Answer» B. n the same direction as current

Discussion

56.	Carbon steel has a residual flux density of 1 Wb/m².
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

57.	As regards dielectric constant εr
A.	the units are farads/m
B.	the units are newton/coulomb
C.	it is dimensionless
D.	the units are farads
Answer» D. the units are farads

Discussion

58.	Assertion (A): For a dielectric, P = ∈₀(∈ᵣ - 1) E.Reason (R): Dipole moment per unit volume is called polarization of dielectric.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» C. A is true but R is false

Discussion

59.	1 Bohr magneton = eh/(4πm) .
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

60.	The resistance of a metallic wire would
A.	increase as f increase
B.	decrease as f increase
C.	remains the same at all frequencies
D.	increase with f up to a certain frequency and then decrease
Answer» B. decrease as f increase

Discussion

61.	The real part of complex dielectric constant and tanδ for a dielectric are 2.1 and 5 x 10¯⁴ at 100 Hz respectively. The imaginary part of dielectric constant at 100 Hz is
A.	1.05 x 10¯³
B.	2.1 x 10¯³
C.	5 x 10¯³
D.	1.05 x 10¯²
Answer» B. 2.1 x 10¯³

Discussion

62.	Assertion (A): Electron concentration n, hole concentration p and charge concentration ni are related by ni² = np.Reason (R): p type semiconductor is obtained by adding trivalent impurity to intrinsic semiconductor.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» C. A is true but R is false

Discussion

63.	The v-i relation for an arc is v = 44 + 30/i . If v = 50 V, i =
A.	10 A
B.	5 A
C.	2 A
D.	0.5 A
Answer» C. 2 A

Discussion

64.	The measurement of Hall coefficient of a semiconductor with one type of charge carriers gives the information about
A.	sign of charge carrier
B.	density of charge carrier
C.	both sign and density of charge carrier
D.	none of the above
Answer» D. none of the above

Discussion

65.	For a core having a relative permeability μᵣ, magnetic dipole moment per unit volume M and field strength H, the flux density B is
A.	B = μᵣ (H + M)
B.	B = μ₀ (H + M)
C.	B = μ₀μᵣ (H + M)
D.	B = μ₀μᵣ (H - M)
Answer» C. B = μ₀μᵣ (H + M)

Discussion

66.	If the diameter of a wire is doubled, its current carrying capacity becomes
A.	one-fourth
B.	half
C.	twice
D.	four times
Answer» E.

Discussion

67.	Consider the following materials1. Nickel2. Silver3. Oxygen4. Aluminium The correct sequence in the order of decreasing permeability is
A.	1, 4, 3, 2
B.	1, 4, 2, 3
C.	4, 1, 3, 2
D.	4, 1, 2, 3
Answer» C. 4, 1, 3, 2

Discussion

68.	An electron (charge -e) is rotating in a circular orbit of radius R, around a proton with charge +e at a constant angular velocity ω. The orbital magnetic dipole moment is
A.	0.5 eω R²
B.	eω R²
C.	2 eω R²
D.	0.5 eω R³
Answer» B. eω R²

Discussion

69.	M = (μᵣ - 1)H.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

70.	Assertion (A): If an atom of polarizability a is placed in homogeneous field E, the energy stored is 0.5 αE².Reason (R): Capacitance of an isolated conducting sphere R in vacuum is 4 π∈₀ R farads.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» B. Both A and R are true but R is not correct explanation of A

Discussion

71.	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.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» B. Both A and R are true but R is not correct explanation of A

Discussion

72.	As regards ∈₀ and ∈ᵣ (absolute and relative permittivity)
A.	both ∈₀ and ∈ᵣ can be interpreted in terms of atomic properties of medium
B.	only ∈ᵣ can be interpreted in terms of atomic properties of medium
C.	only ∈₀ can be interpreted in terms of atomic properties
D.	∈ᵣ has no physical significance
Answer» C. only ∈₀ can be interpreted in terms of atomic properties

Discussion

73.	A dielectric of relative permittivity ∈ᵣ is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by
A.	P = constant
B.	P = ∈₀ E
C.	P = ∈₀(∈ᵣ - 1) E
D.	P = ∈ᵣ E
Answer» D. P = ∈ᵣ E

Discussion

74.	The units of μ₀ and μᵣ are
A.	H/m for both
B.	H/m for μᵣ and no units for μ₀
C.	H/m for μ₀ and no units for μᵣ
D.	Wb/m for μ₀ and no units for μᵣ
Answer» D. Wb/m for μ₀ and no units for μᵣ

Discussion

75.	Assertion (A): ∈ᵣ can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.Reason (R): Capacitance of a parallel plate capacitor = Ɛ₀ƐᵣA/d .
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» B. Both A and R are true but R is not correct explanation of A

Discussion

76.	The wavelength of light emitted by GaAs laser is 8670 x 10¯¹ᴼ m. If h = 6.626 x 10¯³⁴ Js, velocity of light = 3 x 10⁸ m/s and eV = 1.602 x 10¯¹⁹ J, the energy gap in GaAs is
A.	0.18 eV
B.	0.7 eV
C.	1.43 eV
D.	2.39 eV
Answer» D. 2.39 eV

Discussion

77.	The heat developed per m³ per second (W) in a conductor having a conductivity σ and a field E is
A.	W = σE²
B.	W = σE
C.	W = E²/σ
D.	W = (σE)^0.5
Answer» B. W = σE

Discussion

78.	The carrier mobility in a semiconductor is 0.4 m²/Vs. Its diffusion constant at 300 K will be (in m²/s)
A.	0.40
B.	0.16
C.	0.04
D.	0.01
Answer» E.

Discussion

79.	The spin angular momentum along a given direction is either +h/4π or -h/4π .
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

80.	If B, H and M denote flux density, field intensity and magnetisation, B = μ₀ (H + M).
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

81.	Consider the following statements 1. An iron cored choke is non linear and passive device.2. A carbon resistor kept in sunlight is a time invariant and passive device.3. A dry cell is a time varying and active device.4. An air capacitor is time invariant and passive device. Of these statements
A.	1, 2, 3 and 4 are correct
B.	1, 2, 3 are correct
C.	1, 2, 4 are correct
D.	2 and 4 are correct
Answer» B. 1, 2, 3 are correct

Discussion

82.	Assertion (A): Metals are better heat conductors than insulators.Reason (R): If dT/dx is temperature gradient, Q is heat flow density and K is thermal conductivity, then Q = - K (dT/dx).
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» C. A is true but R is false

Discussion

83.	In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as
A.	Lattice constant
B.	Lorentz number
C.	Lanevin function
D.	Larmor number
Answer» C. Lanevin function

Discussion

84.	For dielectrics in alternating field, polarizability αe is a complex quantity. The imaginary part of ae is zero for
A.	ω = 0
B.	ω → ∞
C.	ω = 0 and ω → ∞
D.	ω = natural frequency ω₀
Answer» D. ω = natural frequency ω₀

Discussion

85.	Which of the following are true for relative dielectric constant?1. It is dimensionless.2. It is equal to 1 for vacuum.3.It is equal to 1 for all substances.
A.	1 and 2 only
B.	2 and 3 only
C.	1 and 3 only
D.	1, 2 and 3
Answer» B. 2 and 3 only

Discussion

86.	A copper specimen has resistivity equal to 1.8 x 10¯⁸ ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be
A.	1.6 x 10¯⁸ Ω-m
B.	2 x 10¯⁸ Ω-m
C.	3 x 10¯⁸ Ω-m
D.	6 x 10¯⁸ Ω-m
Answer» E.

Discussion

87.	Assertion (A): Magnetic susceptibility of copper is -0.5 x 10¯⁵.Reason (R): Copper is diamagnetic material.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» B. Both A and R are true but R is not correct explanation of A

Discussion

88.	A parallel plate capacitor having C = 200 x 10¯¹² F has loss dielectric having tan δ = 4 x 10¯⁴. At an ac voltage of f = 10⁶ Hz and peak value 2 V, the dielectric losses are
A.	10¯⁸ W
B.	10¯⁶ W
C.	10¯⁴ W
D.	10¯² W
Answer» C. 10¯⁴ W

Discussion

89.	Which capacitor-store higher amount of energy?
A.	Air capacitor
B.	Paper capacitor
C.	Mica capacitor
D.	Plastic film capacitor
Answer» D. Plastic film capacitor

Discussion

90.	Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic.Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions tc are related as λ = vTc.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» C. A is true but R is false

Discussion

91.	Consider the following statement: In case of a superconductor1. B = 02. μᵣ is high3. diamagnetism is high4. transition temperature varies with isotopic mass. Of the above statements
A.	1 and 2 are correct
B.	2, 3, 4 are correct
C.	1, 3, 4 are correct
D.	2, 4 are correct
Answer» D. 2, 4 are correct

Discussion

92.	A rare gas having N atoms/m³ is subjected to an electric field E. The electric dipole moment per unit volume is proportional to N and E.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

93.	Permeability is analogous to
A.	resistivity
B.	retentivity
C.	conductivity
D.	coercivity
Answer» D. coercivity

Discussion

94.	When an atom of polarizability a is placed in an electric field E, the energy stored in atom is 0.5 α E².
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

95.	Magnetisation of a material is the magnetic dipole moment per m³.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

96.	Assertion (A): In an intrinsic semiconductor J = (μn x μp)eni.Reason (R): Intrinsic charge concentration ni at temperature T is given by ni² = A₀ T³ e^(-EG0/kT).
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» C. A is true but R is false

Discussion

97.	The units for ∈ᵣ are
A.	Farads
B.	Farads/m
C.	kV/mn
D.	no units
Answer» E.

Discussion

98.	If v is the velocity of electron, tc is the average time between collisions, the mean free path λ = vtc.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

99.	Assertion (A): For a magnetic material M = (μᵣ - 1) H, where M is magnetic dipole moment/m³, H is field intensity A/m and μᵣ is relative permeability.Reason (R): μᵣ can have any value from 0 to hundreds of thousands.
A.	Both A and R are true and R is correct explanation of A
B.	Both A and R are true but R is not correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» D. A is false but R is true

Discussion

100.	A liquid has N permanent dipoles μᵨ per unit volume and has been subjected to dc field for a long time such that orientation polarization is P₀. At t = 0, the field is suddenly removed, then polarization
A.	will remain constant at P₀
B.	will become zero at t = 0
C.	will delay to zero with a time constant
D.	either b or c
Answer» D. either b or c

Discussion

Explore topic-wise MCQs in Electronics & Communication Engineering.

For a polyatomic gas, the equation relating dielectric constant ∈r with molecular properties is

A dielectric of relative permittivity ∈r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by

An iron specimen has µr = 1000 when B = 0.3 T. If B = 0.35 T, µr

In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will

Hall effect is observed in a specimen (metal or semi conductor) when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is

Carbon steel has a residual flux density of 1 Wb/m².

As regards dielectric constant εr

Assertion (A): For a dielectric, P = ∈₀(∈ᵣ - 1) E.Reason (R): Dipole moment per unit volume is called polarization of dielectric.

1 Bohr magneton = eh/(4πm) .

The resistance of a metallic wire would

The real part of complex dielectric constant and tanδ for a dielectric are 2.1 and 5 x 10¯⁴ at 100 Hz respectively. The imaginary part of dielectric constant at 100 Hz is

Assertion (A): Electron concentration n, hole concentration p and charge concentration ni are related by ni² = np.Reason (R): p type semiconductor is obtained by adding trivalent impurity to intrinsic semiconductor.

The v-i relation for an arc is v = 44 + 30/i . If v = 50 V, i =

The measurement of Hall coefficient of a semiconductor with one type of charge carriers gives the information about

For a core having a relative permeability μᵣ, magnetic dipole moment per unit volume M and field strength H, the flux density B is

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

Consider the following materials1. Nickel2. Silver3. Oxygen4. Aluminium The correct sequence in the order of decreasing permeability is

An electron (charge -e) is rotating in a circular orbit of radius R, around a proton with charge +e at a constant angular velocity ω. The orbital magnetic dipole moment is

M = (μᵣ - 1)H.

Assertion (A): If an atom of polarizability a is placed in homogeneous field E, the energy stored is 0.5 αE².Reason (R): Capacitance of an isolated conducting sphere R in vacuum is 4 π∈₀ R farads.

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.

As regards ∈₀ and ∈ᵣ (absolute and relative permittivity)

A dielectric of relative permittivity ∈ᵣ is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by

The units of μ₀ and μᵣ are

Assertion (A): ∈ᵣ can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.Reason (R): Capacitance of a parallel plate capacitor = Ɛ₀ƐᵣA/d .

The wavelength of light emitted by GaAs laser is 8670 x 10¯¹ᴼ m. If h = 6.626 x 10¯³⁴ Js, velocity of light = 3 x 10⁸ m/s and eV = 1.602 x 10¯¹⁹ J, the energy gap in GaAs is

The heat developed per m³ per second (W) in a conductor having a conductivity σ and a field E is

The carrier mobility in a semiconductor is 0.4 m²/Vs. Its diffusion constant at 300 K will be (in m²/s)

The spin angular momentum along a given direction is either +h/4π or -h/4π .

If B, H and M denote flux density, field intensity and magnetisation, B = μ₀ (H + M).

Consider the following statements 1. An iron cored choke is non linear and passive device.2. A carbon resistor kept in sunlight is a time invariant and passive device.3. A dry cell is a time varying and active device.4. An air capacitor is time invariant and passive device. Of these statements

Assertion (A): Metals are better heat conductors than insulators.Reason (R): If dT/dx is temperature gradient, Q is heat flow density and K is thermal conductivity, then Q = - K (dT/dx).

In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as

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

Which of the following are true for relative dielectric constant?1. It is dimensionless.2. It is equal to 1 for vacuum.3.It is equal to 1 for all substances.

A copper specimen has resistivity equal to 1.8 x 10¯⁸ ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be

Assertion (A): Magnetic susceptibility of copper is -0.5 x 10¯⁵.Reason (R): Copper is diamagnetic material.

A parallel plate capacitor having C = 200 x 10¯¹² F has loss dielectric having tan δ = 4 x 10¯⁴. At an ac voltage of f = 10⁶ Hz and peak value 2 V, the dielectric losses are

Which capacitor-store higher amount of energy?

Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic.Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions tc are related as λ = vTc.

Consider the following statement: In case of a superconductor1. B = 02. μᵣ is high3. diamagnetism is high4. transition temperature varies with isotopic mass. Of the above statements

A rare gas having N atoms/m³ is subjected to an electric field E. The electric dipole moment per unit volume is proportional to N and E.

Permeability is analogous to

When an atom of polarizability a is placed in an electric field E, the energy stored in atom is 0.5 α E².

Magnetisation of a material is the magnetic dipole moment per m³.

Assertion (A): In an intrinsic semiconductor J = (μn x μp)eni.Reason (R): Intrinsic charge concentration ni at temperature T is given by ni² = A₀ T³ e^(-EG0/kT).

The units for ∈ᵣ are

If v is the velocity of electron, tc is the average time between collisions, the mean free path λ = vtc.

Assertion (A): For a magnetic material M = (μᵣ - 1) H, where M is magnetic dipole moment/m³, H is field intensity A/m and μᵣ is relative permeability.Reason (R): μᵣ can have any value from 0 to hundreds of thousands.

A liquid has N permanent dipoles μᵨ per unit volume and has been subjected to dc field for a long time such that orientation polarization is P₀. At t = 0, the field is suddenly removed, then polarization