125 + Interview Questions in Materials and Components in electronics and communication engineering Page 1 InterviewSolution

1.	If denotes principal quantum number, the angular quantum number = 0, 1... (n - 1).
Answer» Angular quantum number determines the angular momentum of electron.

Discussion

2.	A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will
Answer» Bakelite has higher permittivity than air.

Discussion

3.	As per Matthiessen's rule, the total resistivity of a conductor can be written as = + T, where and are constants and T is absolute temperature. At very low temperatures
Answer» At very low temperatures a T → 0. Since resistivity has a finite value even at low temperature, a T < ri.

Discussion

4.	A single layer air cored coil has turns and inductance L. If a new coil is formed by having 2 turns while keeping the coil length and diameter the same, the new inductance is
Answer» Inductance is proportional to square of number of turns.

Discussion

5.	An electron shell corresponding to principal quantum number can contain a maximum of
Answer» The electron shell corresponding to the principal quantum number can contain no more than 2n2 electrons.

Discussion

6.	The iron core of a coil is removed so that it becomes an air cored coil. Its inductance will
Answer» Because magnetic flux will decrease.

Discussion

7.	In an hydrogen atom, an electron moves in the field of a proton. The stability of orbit requires equilibrium between coulomb's force and centrifugal force.
Answer» Orbit is stable only if the two forces are equal and opposite.

Discussion

8.	The units for electric dipole moment are
Answer» It is product of charge and distance.

Discussion

9.	The temperature coefficient of resistivity of semiconductors is
Answer» Resistance of semiconductors decreases with increase in temperature.

Discussion

10.	In a polyatomic gas, the types of polarization which exist together are
Answer» All the three types of polarization exist in polyatomic gases.

Discussion

11.	At T = 0, the resistivity of a perfect single crystal of a metal is
Answer» At absolute zero temperature resistivity of metals is zero.

Discussion

12.	Semiconductors have a positive temperature coefficient of resistivity.
Answer» In semiconductors the temperature coefficient of resistivity is negative.

Discussion

13.	From a homogeneous and isotropic dielectric material of dielectric constant ∈, a small volume element is taken out creating a cavity. The field can be kept homogeneous if D. (i.e., electric flux density inside the cavity) and D (i.e., electric flux density outside the cavity) are such that
Answer» Since the field is homogeneous .

Discussion

14.	Figure shows a composite capacitor. If C, C, C are the capacitances of capacitors A, B, C, the overall capacitance C is
Answer» B and C are in series and A is in parallel with this combination.

Discussion

15.	For an insulating material, dielectric strength and dielectric losses should be
Answer» An insulating material should have high dielectric strength and low losses.

Discussion

16.	For a given value of principle quantum number, the number of possible electronic states are
Answer» The total number of states corresponding to a given value of n is equal to (2l + 1) = 1 + 3 + .... + [2(n-1) + 1] = n2.

Discussion

17.	Electrical conductivity of metals expressed in ohm m is of the order of
Answer» Conductivity is reciprocal of resistivity. Since resistivity of metals is around 10-7 ohm-m, conductivity is about 107 ohm-1 m-1. So 105 is the nearest value.

Discussion

18.	An homogeneous dielectric material is subjected to an electric field E. If a small cavity is made inside the material, the electric field intensity inside and outside the cavity are different.
Answer» The electric field intensity inside and outside the cavity are equal.

Discussion

19.	A dielectric is subjected to alternating field. The dielectric losses are potential to
Answer» Absorption of energy is proportional to imaginary part of complex dielectric constant.

Discussion

20.	The number of tightly bound electrons in silicon atom are
Answer» Silicon has 14 electons and 4 valence electrons. The 10 electrons in the inner orbits are tightly bound.

Discussion

21.	In its lowest state, the electron is bound to the field of proton by an energy equal to
Answer» 13.6 eV is required to ionize hydrogen atom.

Discussion

22.	A parallel plate capacitor has area of plate A and plate separation . Its capacitance is C. A metallic plate P of area A and negligible thickness is added as shown in Figure. The new value of capacitance is
Answer» The new configuration has two capacitors in series and the capacitance of each is 2C.

Discussion

23.	A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
Answer» As temperature is decreased, resistance of conductors decreases and resistance of semiconductors increases.

Discussion

24.	The units for ∈ are
Answer» ∈r is only a numeric. Hence no units.

Discussion

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

Discussion

26.	The chemical properties of atoms are determined by all the electrons and their configuration.
Answer» Chemical properties are governed by valence electrons only.

Discussion

27.	Nichrome is used for
Answer» Because heater coil must be made of high resistivity material.

Discussion

28.	At a very low temperature, a semiconductor
Answer» Semi conductor becomes insulator at very low temperature.

Discussion

29.	As the temperature of semiconductor is increased
Answer» As temperature increases, conductivity of semi- conductors increases.

Discussion

30.	In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be
Answer» Because cast iron has lower permeability than silicon steel.

Discussion

31.	The electric dipole moment of a neutral system of point charges Q, Q.... is Qr . The charges Q
Answer» The system is neutral and hence sum is zero.

Discussion

32.	Semi conducting materials are all
Answer» Many compounds also show semiconducting properties.

Discussion

33.	A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be
Answer» Inductance is proportional to square of number of turns.

Discussion

34.	When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ∈ - ∈ . In such materials, the dielectric losses under alternating stress is proportional
Answer» The imaginary part of ∈r gives rise to absorption of energy.

Discussion

35.	For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in
Answer» It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.

Discussion

36.	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
Answer» Since the dimension of plates is scaled down by K, the area decreases by a factor of K2, the distance between plates decreases by a factor of K. Therefore, capacitance changes to . The selectivity will not be affected.

Discussion

37.	If , , are the mass, velocity and radius of orbit of electron and is Planck's constant, quantum condition for electron's orbit is
Answer» For stable circular orbit angular momentum is equal to integer times .

Discussion

38.	As per Bohr's postulate, only those circular orbits are stable for which the angular momentum is equal to an integer times .
Answer» It is a quantum condition postulated by Bohr.

Discussion

39.	Inductors used at V.H.F. are made using
Answer» Thin film technique ensure low hysteresis and eddy current losses.

Discussion

40.	In a metal, the drift velocity of electrons in the presence of a electric field E is
Answer» Drift velocity is proportional to field strength.

Discussion

41.	When a material becomes a superconductor, its resistivity becomes
Answer» A superconductor has zero resistance.

Discussion

42.	In a piezoelectric crystal, the application of mechanical force will cause
Answer» Piezoelectric materials permit conversion of mechanical force into electrical energy.

Discussion

43.	For a multiplate capacitor having plates, A as area of each plate, the capacitance is proportional to
Answer» If the number of plates is n, the number of capacitors is (n - 1).

Discussion

44.	Ferrites have
Answer» Resistivity of ferrites is very high as compared to that of iron. Hence eddy curretns are much less.

Discussion

45.	If a piece of wood is placed in a magnetic field
Answer» Wood is non-magnetic.

Discussion

46.	The apparent capacitance at a high angular frequency ω of an air cored capacitor having capacitance C and inductance L is given by
Answer» The combination can be represented as L and C in series. . Therefore, .

Discussion

47.	The number of valence electrons in donor impurity are
Answer» Donor impurity has 5 valence electrons (while silicon has 4 valence electrons). Hence donor impurity can donate electrons.

Discussion

48.	In a true valence crystal, the bonding between the atoms is accomplished by the sharing of valence electrons.
Answer» Sharing of valence electons is a characteristic of true valence crystal.

Discussion

49.	The conductivity of intrinsic semiconductor is given by
Answer» For intrinsic semiconductor, Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).

Discussion

50.	The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all other quantities remaining the same, the self inductance will be
Answer» Inductance is inversely proportional to the core length.

Discussion

Explore topic-wise InterviewSolutions in .

If denotes principal quantum number, the angular quantum number = 0, 1... (n - 1).

A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will

As per Matthiessen's rule, the total resistivity of a conductor can be written as = + T, where and are constants and T is absolute temperature. At very low temperatures

A single layer air cored coil has turns and inductance L. If a new coil is formed by having 2 turns while keeping the coil length and diameter the same, the new inductance is

An electron shell corresponding to principal quantum number can contain a maximum of

The iron core of a coil is removed so that it becomes an air cored coil. Its inductance will

In an hydrogen atom, an electron moves in the field of a proton. The stability of orbit requires equilibrium between coulomb's force and centrifugal force.

The units for electric dipole moment are

The temperature coefficient of resistivity of semiconductors is

In a polyatomic gas, the types of polarization which exist together are

At T = 0, the resistivity of a perfect single crystal of a metal is

Semiconductors have a positive temperature coefficient of resistivity.

From a homogeneous and isotropic dielectric material of dielectric constant ∈, a small volume element is taken out creating a cavity. The field can be kept homogeneous if D. (i.e., electric flux density inside the cavity) and D (i.e., electric flux density outside the cavity) are such that

Figure shows a composite capacitor. If C, C, C are the capacitances of capacitors A, B, C, the overall capacitance C is

For an insulating material, dielectric strength and dielectric losses should be

For a given value of principle quantum number, the number of possible electronic states are

Electrical conductivity of metals expressed in ohm m is of the order of

An homogeneous dielectric material is subjected to an electric field E. If a small cavity is made inside the material, the electric field intensity inside and outside the cavity are different.

A dielectric is subjected to alternating field. The dielectric losses are potential to

The number of tightly bound electrons in silicon atom are

In its lowest state, the electron is bound to the field of proton by an energy equal to

A parallel plate capacitor has area of plate A and plate separation . Its capacitance is C. A metallic plate P of area A and negligible thickness is added as shown in Figure. The new value of capacitance is

A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of

The units for ∈ are

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

The chemical properties of atoms are determined by all the electrons and their configuration.

Nichrome is used for

At a very low temperature, a semiconductor

As the temperature of semiconductor is increased

In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be

The electric dipole moment of a neutral system of point charges Q, Q.... is Qr . The charges Q

Semi conducting materials are all

A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be

When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ∈ - ∈ . In such materials, the dielectric losses under alternating stress is proportional

For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in

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

If , , are the mass, velocity and radius of orbit of electron and is Planck's constant, quantum condition for electron's orbit is

As per Bohr's postulate, only those circular orbits are stable for which the angular momentum is equal to an integer times .

Inductors used at V.H.F. are made using

In a metal, the drift velocity of electrons in the presence of a electric field E is

When a material becomes a superconductor, its resistivity becomes

In a piezoelectric crystal, the application of mechanical force will cause

For a multiplate capacitor having plates, A as area of each plate, the capacitance is proportional to

Ferrites have

If a piece of wood is placed in a magnetic field

The apparent capacitance at a high angular frequency ω of an air cored capacitor having capacitance C and inductance L is given by

The number of valence electrons in donor impurity are

In a true valence crystal, the bonding between the atoms is accomplished by the sharing of valence electrons.

The conductivity of intrinsic semiconductor is given by

The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all other quantities remaining the same, the self inductance will be