electronics and Communications objective questions

electronics and Communications objective questions

1. When BCC iron is heated, it changes to FCC iron resulting in
(a)contraction -in volume
(b) increase in volume
(c)no change in volume
(d) crack in the material
2. When copper is added to silver in small quantity so as to form an alloy, the resistivity of such an alloy is
(a) equal to the resistivity of copper
(b) equal to the resistivity of silver
(c) greater than the resistivity of copper
(d) in between the resistivity of silver and copper
3. Match List-I (Materials) with List-II (Applications of materials) and select the correct answer using codes given below the lists:
List-I List -II
(Materials) (Applications of materials)
A. Aluminum 1. Current carrying spring
B. Phosphor Bronze 2. Heating element
C. Carbon 3. Commutator brush
D. Ni chrome 4. Telephone chords and trolley wires
Codes:
A B C D
4 3 1 2
(b) 2 1 3 4
(c) 4 1 3 2
(d) 2 3 1 4
4. When a semiconductor bar is heated at one end, a voltage across the bar is developed. If the heated end is positive, the semiconductor is ?
(a) p-type
(b) n-type
(c) intrinsic
(d) highly degenerate
5. The conductivity of a semiconductor crystal due to any current carrier is NOT proportional to
(a.) mobility of the carrier
(b) effective density of states in the conduction band
(c) electronic charge
(d) surface states in the semiconductor
6. Amplification of ultrasonic waves is possible in a piezoelectric semiconductor under applied electric field. The basic phenomenon involved is known as
(a) Electrostriction
(b) Acousto-optic interaction
(c)Acoustic-electric interaction
(d) Stimulated Brillouin scattering
7. Piezoelectric quartz crystal resonators find application where
(a) signal amplification is required
(b) rectification of the signal is required
(c) signal frequency control is required
(d)modulation of signal is required
8. When certain percentage of silicon is added to iron, the resistivity of the iron increase by a factor of 5. If a transformer core is made out of this iron, as compared to the previous value when silicon was not added, the eddy current loss will be
(a) 77%
(b) 80%
(c) 83%
(d) 86%
9. Which of the following are the properties of ferromagnetic domains?
1. Permanent magnetisation
2. Atomic moments in individual domains are all aligned neither parallel to nor perpendicular to one another below Curie point temperature
3. Each domain is magnetically saturated
4. Above Curie temperature, domains disrupt
Select the correct answer using the codes given below :
Codes:
(a) 1 and 3
(b) 2 and 4
(c)1, 3 and 4
(d) 3 and 4
10. Match List-I (Insulators) with List-II (Resistivity) and select the correct answer
using codes given below the lists:
List-I List-II
(Insulators) (Resistivity)
A. Bakelite 1.10⁵ ohm-cm
B. Window glass 2.10⁹ ohm-cm
C. Pure silica 3.10¹³ ohm-cm
D; Mica 4. 10¹⁷ ohm-cm
Codes:
A B C D
(a) 4 3 1 2
(b) 1 2 4 3
(c) 4 2 1 3
(d) 1 3 4 2
11. Which of the following phenomena is most important when foodstuff is cooked in
a microwave oven?
(a) Resistive Joule heating
(b) Induction heating
(c)Dielectric heating
(d) Radiation heating
12. The frequency dependence of electronic polarizability of a dielectric is obtained by solving the equation:
mx=- ax- 2bx – 2E₀ cos wt. Consider the following statements:
In this equation,
1. a is the restoring force constant, the expression for which is obtained from Coulomb’s law
2. m is the combined mass of electrons and nucleus
3. b is the damping constant occurring due to emission of electromagnetic radiation
4 m x term arises due to altered velocity of electrons orbiting the nucleus in presence of field.
Which of the above statements are correct?
(a)1 and 2
(b) 1 and 3
(c)1,2 and 4
(d) 2,3 and 4
13. The correct sequence of the following in the increasing order of the values of
permittivity is
(a) Air, Vacuum, TaO₂ Glass
(b) Air, Vacuum, Glass, TaO₂
(c) Vacuum, Air, TaO₂ Glass
(d) Vacuum, Air, Glass, TaO₂
14. Match List-I (Polarization process) with List-Il (Approximate frequency) and select the correct answer using codes given below the lists:
List-I List-II
(Polarization process) (Approximate frequency)
A. Electronic polarization 1. 10² Hz
B. Ionic polarization 2. 10⁵ Hz
C. Orientation polarization 3. 10¹³ Hz
D. Space-charge polarization 4. 10¹⁵ Hz
Codes:
A B C D
a) 1 2 3 4
(b) 4 3 2 1
(c) 1 3 2 4
(d) 4 2 3 1
15. Which material among the following possesses excellent dielectric properties and good reliability for use in making capacitors?
(a)Silicon monoxide
(b) Silicon dioxide
(c) Tin oxide
(d) Chromium oxide
16. The most suitable material for making an LDR (Light dependent resistor) is a semiconductor material having
(a) Eg>> hv
(b) Eg > hv
(c) Eg=hV
(d) Eg<
17. Which one of the following is an essential components of electromechanical
relays?
(a)Graphite rod
(b) LED
(c)An electromagnet
(d) MOSFET
18. In a degenerate semiconductor, the majority carriers are controlled by
(a) Fermi-Dirac statistics
(b) Maxwell-Boltzmann statistics
(c) Bose-Einstein (B-E) statistics
(d) Pauli’s exclusion principle
19. Fermions are the particles, which obey
(a)Maxwell-Boltzmann’s statistics
(b)Bose-Einstein’s statistics
(c Heisenberg’s uncertainty principle
(d Pauli’s exclusion principle
20. Excess carriers are generated in a sample of N-type semiconductor by shining
light at one end. The current flow in the sample will be made up of
(a) diffusion flow of carriers
(b) drift flow of carriers
(c) both diffusion and drift flow of carriers
(d) neither diffusion nor drift flow of carriers
Answers :
1 : a
2: c
3: c
4: b
5: d
6: a
7: c
8: b
9: c
10: b
11 : b
12 : b
13: b
14: b
15 : d
16 : d
17 : c
18 : a
19 : d
20: a