Bharat Sanchar Nigam Limited BSNL Technical Assistant- TTA Electronics and electrical solved questions for practice
BSNL OBJECTIVE TYPE QUESTIONS FOR PRACTICE
1. The electrical conductivity of metals is typically of the order of (in ohm-1 m-1)
(A) 107 (Ans)
(B) 105
(C) 10-4
(D) 10-6
2. There electronic configuration of carbon is
(A) 1s2 2s2
(B) 1s2 2s2 2p6 2s2
(C) 1s2 2s2 2p6
(D) 1s2 2s2 2p2 (Ans)
3. Which law is synonymous to the occurrence of diamagnetism?
(A) Ampere’s law
(B) Maxwell’s law
(C) Coulomb’s law
(D) Lenze’s law (Ans)
4. Which of the following are piezo-electric substances:
1. Barium titanate
2. Lead titanate
3. Lead triconate
4. Cadmium sulphate
(A) 1,2 and 4
(B) 1,3 and 4
(C) 1,2 and 3 (Ans)
(D) 2,3 and 4
5. The temperature below which certain materials are anti-ferromagnetic and above which they are paramagnetic is called
(A) Weiss temperature
(B) Curie temperature
(C) Neel temperature (Ans)
(D) Double point temperature
6. Pure metals generally have
(A) high conductivity and low temperature co-efficient
(B) high conductivity and large temperature co-efficient (Ans)
(C) low conductivity and zero temperature co-efficient
(D) low conductivity and high temperature co-efficient
7. Magnetostriction
(A) induced magnetism
(B) volume changes accompanying (Ans)
(C) rate of magnetisation
(D) rate of loss of magnetism
8. When ne and nh are the electron and hole densities, and µe and µh are the carrier mobilities, the Hall co-efficient is positive when,
(A) nh µh > ne µe
(B) nh µh2> ne µ2e (Ans)
(C) nh µh < µe
(D) nh µh2> ne µ2e
9. Semi-conductor A has a higher band gap than semi-conductor B. If both A and B have the same dimensions, the same number of electrons at a given temperature and the same electron and hole mobilities, then
(A) A has the same number of holes as B
(B) A has a larger number of holes than B (Ans)
(C) A has a less number of holes than B
(D) Any of the above statements at (A), (B) or (C) could be true
10. Which of the following crystallographic defects contributes to electronic defects?
1. Thermal vibration
2. Point defects
3. Line defects
4. Surface defects
Select the correct answer using the codes given below
(A) 1,2 and 3 (Ans)
(B) 2,3 and 4
(C) 1,3 and 4
(D) 1,2 and 4
11. Above the curie temperature, the hysteresis loop of a ferroelectric material can be described by a
(A) parabola
(B) cycloid (Ans)
(C) straight line
(D) point
12. Orientational polarizations is
(A) inversely proportional to temperature and proportional to the square of the permanent dipole moment (Ans)
(B) proportional to temperature as well as to the square of the permanent dipole moment
(C) proportional to temperature and inversely proportional to the square of the permanent dipole moment
(D) inversely proportional to temperature as well as to the square of dipole moment
13. In a piezoelectric crystal oscillator, the oscillation or tuning frequency is linearly proportional to the
(A) mass of the crystal
(B) square root of the mass of the crystal
(C) square of the mass of the crystal
(D) inverse of the square root of the mass of the crystal (Ans)
14. Some of electrons are injected into the interior of a conductor surrounded by an insulator.
The injected electrons will
(A) distribute themselves uniformly
(B) distribute themselves randomly
(C) be confined at the point of injection
(D) travel to the surface of the conductor (Ans)
15. The isotope effect predicts that the super-conducting transition temperature should be proportional to (M is the atomic mass)
(A) M
(B) 1/M
(C) 1/√M (Ans)
(D) √M
16. Consider the following statements : In the case of diamagnetic materials, the magnetic susceptibility is
1. Positive
2. Negative
3. Independent of temperature
4. Inversely proportional to temperature of these statements
(A) 1 and 3 are correct
(B) 2 and 3 are correct (Ans)
(C) 1 and 4 are correct
(D) 2 and 4 are correct
17. A small saw cut is made in a permanent magnet of toroidal shape. Which of the following are true for H0, if H0 is the magnetic field in the air-gap and Hi is that inside the magnet?
1. H0 < │Hi│
2. H0 > │Hi│
3. H0 is in the same direction as Hi
4. H0 and Hi are in opposite directions
Select the correct answer using the codes given below:
Codes:
(A) 1 and 3
(B) 1 and 4
(C) 2 and 3 (Ans)
(D) 2 and 4
18. Silicon contains 5*1028 atoms per cubic meter. If it is doped with two parts per million of arsenic , then the electron density at room temperature will be approximately.
(A) 4*1023 m3
(B) 1023 m-3 (Ans)
(C) 2*106 m-3
(D) 104 m-3
19. In a certain temperature range, the electrical conductivity of a semi-conductor increases with increase in temperature. This is because
(A) both carrier concentration and mobilty of carriers increase with increasing temperature
(B) both carrier concentration and mobility of carriers decrease with increasing temperatures
(C) the carrier concentration increase substantially, but the mobility of carriers decreases with increase in temperature (Ans)
(D) the carrier concentration remains constant but the mobility of carriers increases in temperature
20. The Hall-effect voltage in intrinsic silicon
(A) is positive
(B) is zero
(C) is negative (Ans)
(D) changes sign on application of magnetic field
21. The function of oxide layer in IC fabricaton is
1. to mask against diffusion
2. to insulate surface electricity
3. to produce chemical stable surface
4. to increase the metling point
Consider above statement then correct are :
(A) 1, 2 and 3 (Ans)
(B) 2, 3 and 4
(C) 3, 4 and 1
(D) 3 and 4 only
22. Consider a single crystal of an intrinsic semi-conductor. The number of free carriers at the fermi level at room temperature is
(A) half the total number of electrons in the crystal
(B) half the number of free electrons in the crystal (Ans)
(C) half the number of atoms in the crystal
(D) zero
23. If the molecular structure and density of the material are known, then which of the following material parameters may be determined from the εr versus 1/T plot?
(A) Sum of electronic and ionic polarizabilities (Ans)
(B) Lattice constant
(C) Breakdown voltage
(D) Loss constant
24 The electron relaxation time of metal A is 2.7*10-4 sec that of B is 1.35*10-4 sec. The ratio of resistivity of B to resistivity of A will be
(A) 4.0
(B) 2.0 (Ans)
(C) 0.5
(D) 0.25
25. Electrical conductivity of copper reduces with addition of a small amount of nickel because
(A) the mobility decreases due to creation of new scattering centres for electrons (Ans)
(B) nickel is ferromagnetic
(C) less free electrons are available for conduction
(D) the electrons of copper become bound to nickel atoms and are not free to move
26. Magnetic susceptibility of an ideal Type-I super-conductor in the super-conductivity state is
(A) -8
(B) -1 (Ans)
(C) between 0 and -1
(D) zero
27. When the transition occurs to the super conducting state, the magnetic flux is excluded from the material. This is known as
(A) Magnetophobic effect
(B) Silsbee effect
(C) Meissner effect (Ans)
(D) Copper effect
28. Cu2 MnAl is
(A) piezoelectric
(B) paramagnetic
(C) ferrimagnetic
(D) ferromagnetic (Ans)
29. In an intrinsic semi-conductor, the mobility of electrons in the conduction band is
(A) zero
(B) less than the mobility of holes in the valence band
(C) equal to the mobility of holes in the valence band
(D) greater than the mobility of holes in the valence band (Ans)
30. The effect of doping intrinsic semi- conductors is to
(A) move the fermi level away from the centre of the forbidden band (Ans)
(B) move the fermi level towards the centre of the forbidden band
(C) change the crystal structure of the semi-conductor
(D) keep the fermi level at the middele of the forbidden band
31. The hall co-efficient of sample (A) of a semi-conductor is measured at room temperature. The hall co-efficient of A at room temperature is 4*10-4 m3 colomb-1 . The carrier concentration in sample A at room temperature is
(A) ~ 10-4 m-3
(B) ~ 1024 m-3
(C) ~ 104 m-3
(D) ~ 1022 m-3 (Ans)
32. The hall angle θ of a metal sample is
(A) independent of the magnetic flux density B
(B) independent of the carrier mobility
(C) independent of the density of free carriers
(D) dependent on magnetic flux density, carrier mobility and density of free carriers (Ans)
33. The resistance of a thermistor is 5000 Ω at 200 C and its resistance temperature co-efficient is 0.04/0C. A measurement with a lead resistance of 10 Ω will cause an error of
(A) 0.050 C (Ans)
(B) 0.10 C
(C) 0.40 C
(D) 0.80 C
34. When a solid crystal of sodium is formed, the 3s-band will have
(A) half as many states as the number of atoms (Ans)
(B) same number of states as there are atoms
(C) twice as many states as there are atoms
(D) no states at all
35. The relaxation time (τ) in a perfect dielectric is
(A) 0 (Ans)
(B) 1
(C) 1 < τ ∞
(D) ∞
36. The number of stress co-efficients or constants which characterize a piezoelectric material is
(A) 24 (Ans)
(B) 18
(C) 9
(D) 3
37. Which of the following pair (s) is/are correctly matched?
Material Application
1. Rochelle salt Phonograph
2. Barium titanate Amplifier
3. Quartz Oscillator
Select the correct answer using the codes given below :
(A) only 2
(B) 1 and 2
(C) 1 and 3 (Ans)
(D) 2 and 3
38. The conductivity of a metal at ultraviolet frequency (1014 Hz) approximately equals
(A) infinity
(B) zero
(C) d.c. conductivity
(D) half of d.c. conductivity (Ans)
39. Constantan is an alloy composed of
(A) 86% copper, 12% manganese and 2% nickel
(B) 76% nickel, 21% chromium, 2% manganese and 1% iron
(C) 60% copper and 40% nickel (Ans)
(D) 40% copper and 40% nickel and 20% carbon
40. Some of the characterizing parameters of a material are
1. Magnetic permeability
2. Electron relaxation time
3. Electron effective mass
4. Energy band gap
In case of metals, increase in one of the above parameters decreases its conductivity, while increase in another increase the conductivity. These two parameters are respectively.
(A) 1 and 3
(B) 3 and 2 (Ans)
(C) 4 and 3
(D) 1 and 2
41. What type of magnetic behaviour is observed in a type-I super-conductor?
(A) Perfect diamagnetism (Ans)
(B) Perfect paramagnetism
(C) Perfect ferromagnetism
(D) Perfect ferrimagnetism
42. The super-conducting transition temperature of lead is 7.26 K. If the initial field at OK is 64*103 Amp/m, then the critical field at 5 K is
(A) 0.3364*103 Amp/m
(B) 3.364*103 Amp/m
(C) 33.640*103 Amp/m (Ans)
(D) 336.400*103 Amp/m
43. Match List-I with List-II and select the correct answer using the codes given below the lists :
List-I List-II
(Material) (Classification)
(a) Mgo Fe2O3 1. Piezoelectric material
(b) BaTiO3 2. Ferrimagnetic material
(c) Cobalt 3. Ferromagnetic material
(d) Copper 4. Diamagnetic material
Codes :
(a) (b) (c) (d)
(A) 2 3 4 1
(B) 2 1 3 4
(C) 1 2 4 3
(D) 1 2 3 4
(Ans-B)
44. A paramagnetic material is used in an energy conversion process in which the following events occur:
1. Thermal energy is generated
2. Dipoles are turned
3. Magnetic field is generated
4. Material reacts to oppose it.
The correct sequence of these event is
(A) 3, 4, 2, 1
(B) 1, 4, 2, 3
(C) 1, 2, 4, 3
(D) 3, 2, 4, 1 (Ans)
45. A sample of iron carrying a current is subjected to a magnetic field. Match List-I with List-II to indicate the influence of angle between the magnetic field and current on the resistivity of the sample and select the correct answer using the codes given below the lists:
List-I List-II
(Direction of current) (Electrical resistivity)
(A) Parallel to magnetisation 1. Increase
(B) Perpendicular magnetisation 2. Decrease
3. Unchanged
Codes :
(a) (b)
(A) 1 2
(B) 2 1
(C) 2 3
(D) 3 1
(Ans-D)
46. Some magnetic materials may be classified on the basis of
1. Susceptibility
2. Saturation
3. Spin arrangement
4. Nature of hysteresis loop
5. Domain structure
6. Critical temperature above which it behaves as a paramagnetic material.
Out of these, those which can be used to distinguish between ferri and ferromagnetic matgerials would include
(A) 1, 3 and 4 (Ans)
(B) 2, 3 and 6
(C) 3, 4 and 5
(D) 3, 5 and 6
47. Assuming carrier mobility to be temperature independent, it can be shown that pure Si (Eg = 1.1 eV) and Ge (Eg = 0.7 eV) have the same conductivity at a temperature of
(A) 191 K
(B) 300 K
(C) 471 K
(D) 1470 K (Ans)
48. The processes that can be used to make the steel magnetically softer are
1. Annealing
2. Grain growth
3. Decarburization
4. Quenching
(A) 1, 2 and 3 (Ans)
(B) 2, 3 and 4
(C) 2 and 3 only
(D) 3 and 4 only
49. Polarization is a measure of
(A) dielectric constant per unit volume (Ans)
(B) voltage gradient of produce eslectrical breakdown
(C) product of charge and distance
(D) excess charge density
50 Consider the following semi-conductor diodes
1. Germanium diode
2. Silicon diode
3. Tunnel diode
4. Schottky diode
The correct increasing order of forward voltage drop of these diodes is
(A) 1,3,2,4
(B) 1,2,3,4
(C) 3,4,2,1
(D) 3,1,4,2 (Ans)