Explore topic-wise MCQs in Electronics & Communication Engineering.

This section includes 595 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.

1.

The spin angular momentum along a given direction is either or .

A. True
B. False
Answer» B. False
Discussion
2.

For a diamagnetic material, μr = 1.

A. True
B. False
Answer» B. False
Discussion
3.

If ω0 is the angular frequency of rotation of electron in the absence of magnetic field, the angular frequency ω, when a magnetic field B is acting is ω ≅ ω0 + (e/2m)B.

A. True
B. False
Answer» B. False
Discussion
4.

M = (μr - 1)H.

A. True
B. False
Answer» B. False
Discussion
5.

If e 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 μm of the orbit is |μm| = eωR2.

A. True
B. False
Answer» C.
Discussion
6.

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

A. True
B. False
Answer» B. False
Discussion
7.

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".

A. True
B. False
Answer» B. False
Discussion
8.

If ∈r = ∈r' - j∈r" tan δ = .

A. True
B. False
Answer» B. False
Discussion
9.

The equation D = ∈0∈r E refers only to isotropic materials.

A. True
B. False
Answer» B. False
Discussion
10.

In an homogeneous dielectric subjected to an electric field E, the dipole moment per unit volume is ∈0(∈r - 1) E.

A. True
B. False
Answer» B. False
Discussion
11.

∈0 has no other physical meaning than that of a fundamental conversion factor.

A. True
B. False
Answer» B. False
Discussion
12.

∈r is determined by the atomic structure of the dielectric.

A. True
B. False
Answer» B. False
Discussion
13.

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
14.

Assertion (A): When cathode temperature is increased from 2500 K to 2550 K, thermionic emission current may increase by about 50%.Reason (R): Thermionic emission current ∝ T2 e-Ew/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» B. Both A and R are true but R is not correct explanation of A
Discussion
15.

Assertion (A): Ferromagnetic materials possess ferromagnetic properties only when temperature is less than paramagnetic curie temperature.Reason (R): For a ferromagnetic material for T > θf.

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
16.

Assertion (A): Magnetic susceptibility of diamagnetic materials is much less than that of paramagnetic materials.Reason (R): For diamagnetic as well as paramagnetic materials, μr is nearly equal to 1.

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
17.

Assertion (A): For Diamond, μr = 1Reason (R): Diamond is a 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
18.

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
19.

Assertion (A): If an electron having charge e is revolving in an orbit of radius R and with angular velocity ω, the magnetic dipole moment of orbit is 0.5 eωR2.Reason (R): Orbital angular momentum and magnetic dipole moment are always equal.

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
20.

Assertion (A): In a parallel plate capacitor having area of plate 1 m2 and plate separation 1 m, the capacitance C and resistance R are given by C = ∈0∈'r and R = where ω is frequency, ∈r' and ∈r" are real and imaginary parts of dielectric constant.Reason (R): The imaginary part of electric constant is responsible for dielectric losses.

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
21.

Assertion (A): Dielectric losses are proportional to tan δ.Reason (R): tan δ = where ∈r' and ∈r" denote the real and imaginary parts of ∈r.

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
22.

Assertion (A): If an atom of polarizability a is placed in homogeneous field E, the energy stored is 0.5 aE2.Reason (R): Capacitance of an isolated conducting sphere R in vacuum is 4 p∈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
23.

Assertion (A): In a perfect capacitor, the current density is given by ω ∈0E0∈'rcos(ωt + 90°), where ∈r' is real part of dielectric constant.Reason (R): In a perfect capacitor, dielectric losses are zero.

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
24.

Assertion (A): Ferroelectric materials have spontaneous polarization.Reason (R): Above curie temperature, ∈ = for ferro-electric materials.

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
25.

Assertion (A): In some materials, ∈r is independent of temperature while in others, ∈r depends on temperature.Reason (R): If permanent dipoles are absent, ∈r varies with temperature.

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
26.

Assertion (A): From the slope of the line in Figure, we can find permanent dipole moment of the molecules.Reason (R): Total polarization of a polyatomic gas is given by P = N(ae + ai + μ2p / 3kT)E.

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
27.

Assertion (A): Electronic polarizability increases as atoms becomes larger.Reason (R): For rare gas, ∈0(∈r - 1) E = Nae, where N is number of atoms/m3 and ae is electronic polarizability of 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» C. A is true but R is false
Discussion
28.

Assertion (A): ∈0 has the dimensions of farad per meter.Reason (R): D = ∈0∈r E.

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
29.

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 = .

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
30.

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
31.

Assertion (A): The equation D = ∈0∈rE is applicable only to isotropic materials.Reason (R): In polycrystalline materials, the directional effects are absent.

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
32.

For a superconductor, magnetisation M in a field H is

A. extremely small
B. - H
C. - I
D. zero
Answer» C. - I
Discussion
33.

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
34.

A vacuum parallel plate capacitor is charged. The field between the plates is 2 x 104 V/m. If the space between the plates is filled with a material having ∈r = 10, then the value of field in the dielectric will be

A. 2 x 103 V/m
B. x 104 V/m
C. 210 x 104 V/m
D. 2 x 105 V/m
Answer» B. x 104 V/m
Discussion
35.

Consider the following statement: In case of a superconductor B = 0μr is highdiamagnetism is hightransition 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
36.

The units for ∈r are

A. Farads
B. Farads/m
C. [C].
D. no units
Answer» E.
Discussion
37.

The law that (where K is thermal conductivity, σ is electrical conductivity and T is absolute temperature) for all metals is equal to a universal constant is known as

A. Lorentz law
B. Wiedemann Franz law
C. Curie Weiss law
D. Kittel law
Answer» B. Wiedemann Franz law
Discussion
38.

The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is

A. Q = K(dT/dx)
B. Q = - K(dT/dx)
C. K = Q(dT/dx)
D. dT/dx = - QK
Answer» C. K = Q(dT/dx)
Discussion
39.

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 =
D. W = (σE)0.5
Answer» B. W = σE
Discussion
40.

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

A. 2pP(θ) sin θ dθ = 0
B. 2pP(θ) sin θ dθ = 2
C. 2pP(θ) sin θ dθ = -1
D. 2pP(θ) sin θ dθ = 1
Answer» D. 2pP(θ) sin θ dθ = 1
Discussion
41.

If a metal specimen has n valence electrons per m3 each having charge e and mass m and t is the relaxations time, the conductivity is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
42.

A material has N spins per m3. If Np are the dipoles per m3 parallel to field and Na are the dipoles per m3 anti-parallel to field, the magnetisation is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
43.

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

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
44.

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
45.

The core of a solenoid is made of material of relative permeability μr. A small cavity area dA and length dl is cut in the core. If it is desired that flux density in the cavity should be equal to B0

A. the fields inside and outside the cavity must be equal
B. the field inside the cavity must be made stronger than field outside the cavity
C. the field inside the cavity must be made weaker than the field outside the cavity
D. none of the above
Answer» C. the field inside the cavity must be made weaker than the field outside the cavity
Discussion
46.

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
47.

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
48.

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
49.

A parallel plate capacitor has area of plate equal to 1 m and distance between plates is also 1 m2. The lossy dielectric has a complex dielectric constant ∈r = ∈'r - j ∈"r. If the capacitor is represented by R and C is parallel, then

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
50.

A liquid has N permanent dipoles μp 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