Electronics Engineering Multiple Choice Questions and Answers (MCQs) Part 1:
1. Which of the following statements is correct regarding resistance ?
(a) The resistance of a conductor is the hindrance by which the conductor opposes the flow of current through it.
(b) The resistance of wire is independent of the temperature for most of the materials.
(c) The resistance of a wire does not depend upon its material.
(d) None of the above.
Answer : (a) The resistance of a conductor is the hindrance by which the conductor opposes the flow of current through it.
2. An air-cored inductance is a
(a) linear circuit element because its reactance varies linearly with frequency.
(b) linear circuit element because its current varies linearly with voltage at a fixed frequency.
(c) nonlinear circuit element in view of the possible magnetic saturation of the air core.
(d) nonlinear circuit element in view of the equation v = L (di/dt) involving differentiation.
Answer : (b) linear circuit element because its current varies linearly with voltage at a fixed frequency.
3. Which of the following statements associated with capacitors is wrong?
(a) A capacitor resists an abrupt change in the voltage across it in a manner analogous to the way a spring resists abrupt change in its displacement.
(b) A capacitor resists an abrupt change in the current flowing through it.
(c) It is impossible to change the voltage across a capacitor even if the current through the capacitor by a finite amount in zero time, for this requires infinite current through the capacitor.
(d) A finite amount of energy can be stored in a capacitor even if the current through the capacitor is zero, such as when the voltage across it is a constant.
Answer : (b) A capacitor resists an abrupt change in the current flowing through it.
4. Which of the following statements associated with inductors is wrong ?
(a) An inductor is a sort of short circuit to dc.
(b) An inductor is a sort of open circuit to dc.
(c) An inductor never dissipates energy but only stores it.
(d) A finite amount of energy can be stored in an inductor even if voltage across it is zero, such as when the current through it is constant.
Answer : (b) An inductor is a sort of open circuit to dc.
5. An ideal voltage source should have
(a) large emf.
(b) small emf.
(c) zero resistance.
(d) none of these.
Answer : (c) zero resistance.
6. Ideal current source have
(a) zero internal resistance.
(b) infinite internal resistance.
(c) low value of voltage.
(d) large value of current.
Answer : (b) infinite internal resistance.
7. Superposition theorem is applicable for:
(a) Linear circuits only.
(b) Nonlinear circuits only.
(c) Linear and nonlinear circuits both.
(d) None of these.
Answer : (a) Linear circuits only.
8. While Thevenizing a circuit between two terminals, VTH is equal to
(a) short-circuit terminal voltage.
(b) open-circuit terminal voltage.
(c) net voltage available in the circuit.
(d) emf of the battery nearest to the terminals.
Answer : (b) open-circuit terminal voltage.
9. While determining RTH of a circuit
(a) voltage and current sources should be left as they are.
(b) all sources should be replaced by their source resistances.
(c) all independent current and voltage sources are short-circuited.
(d) none of the above.
Answer : (b) all sources should be replaced by their source resistances.
10. Which of the following statements is/are correct ?
(a) Norton’s equivalent resistance is the same as Thevenin’s equivalent resistance RTH.
(b) Norton’s equivalent is the current equivalent of the network.
(c) The load is connected in parallel to the Norton’s equivalent resistance and Norton’s equivalent current source.
(d) all of the above.
Answer : (d) all of the above.
11. When the power transferred to the load is maximum, the efficiency of power transfer is
(a) 25%.
(b) 75%.
(c) 50%.
(d) 100%.
Answer : (c) 50%.
12. A load is connected to an active network. At the terminals to which the load is connected, Rth = 10 Ω and Vth = 60 V. Then maximum power supplied to the load is
(a) 360 W
(b) 90 W
(c) 60 W
(d) 10 W
Answer : (b) 90 W
13. Total number of electrons that can be accommodated in various electron states in a valence band of a given solid is equal to
(a) atomic number of the solid.
(b) half the number of atoms in the solid.
(c) the number of atoms in the solid.
(d) twice the number of atoms in the solid.
Answer : (a) atomic number of the solid.
14. Width of energy bands depends on which of the following?
(a) Temperature.
(b) Pressure.
(c) Relative freedom of electrons in the crystal.
(d) Mass of atom in the material.
Answer : (a) Temperature.
15. The probability that an electron in a metal occupies the Fermi-level at any temperature (> 0 K) is
(a) 0
(b) 1
(c) 0.5
(d) 1.0
Answer : (b) 1
16. Ohm’s law in point form in field theory can be expressed as
(a) V = RI
(b) J = E/σ
(c) J = σE
(d) R = ρ l/A
Answer : (c) J = σE
17. For insulators, the forbidden gap is of the order of
(a) 5 eV
(b) 1 eV
(c) 0.1 eV
(d) zero
Answer : (a) 5 eV
18. The materials not having negative temperature coefficient of resistivity are
(a) metals.
(b) semiconductors.
(c) insulators.
(d) None of these.
Answer : (a) metals.
19. Typical value of ionisation energy of an electron for an N-type semiconductor can be about
(a) 0.001 eV
(b) 0.01 eV
(c) 1.1 eV
(d) 0.15 eV
Answer : (b) 0.01 eV
20. The bonding forces in compound semiconductors, such as GaAs, arise from
(a) ionic bonding.
(b) metallic bonding.
(c) covalent bonding.
(d) combination of ionic and covalent bonding.
Answer : (c) covalent bonding.
21. The Fermi energy EF of a metal is proportional to (n is the number of free electrons per unit volume of the metal) as
(a) n2
(b) n1/2
(c) n2/3
(d) n3/2
Answer : (c) n2/3
22. Assuming the Fermi level EF to be independent of temperature, EF may be defined as the level with an occupancy probability of
(a) 0%
(b) 50%
(c) 75%
(d) 100%
Answer : (b) 50%
23. In an intrinsic semiconductor, the number of electrons is equal to the number of holes at which temperature ?
(a) 0 K
(b) 0°C
(c) high temperature.
(d) all temperatures.
Answer : (a) 0 K
24. Which one of the following statements is correct?
If the Fermi level lies midway between the conduction and valence bands, then the semiconductor is
(a) intrinsic.
(b) extrinsic.
(c) p-type.
(d) n-type.
Answer : (a) intrinsic.
25. On which of the following factors does the electrical conductivity of a semiconductor depend?
1. Carrier concentration. 2. Carrier mobility. 3. Sign of the carrier.
Select the correct answer using the codes given below:
(a) 1 and 2
(b) 1 and 3
(c) 2 and 3
(d) 1, 2 and 3
Answer : (a) 1 and 2
26. Controlled addition of group III element to an elemental semiconductor results in the formation of
(a) intrinsic semiconductor.
(b) n-type semiconductor.
(c) p-type semiconductor.
(d) degenerate semiconductor.
Answer : (c) p-type semiconductor.
27. Atomic number of silicon is
(a) 12
(b) 13
(c) 14
(d) 15
Answer : (c) 14
28. The bandgap of Silicon at room temperature is
(a) 1.3 eV
(b) 0.7 eV
(c) 1.1 eV
(d) 1.4 eV
Answer : (c) 1.1 eV
29. The mobility of electrons in a material is expressed in units of
(a) V/s
(b) m2/V-s
(c) m2/s
(d) J/K
Answer : (b) m2/V-s
30. n-type silicon is obtained by doping silicon with
(a) Germanium.
(b) Aluminium.
(c) Boron.
(d) Phosphorus.
Answer : (d) Phosphorus.
31. In an n-type silicon crystal at room temperature, which of the following can have a concentration of 4 x 1019 cm-3?
(a) Silicon atoms.
(b) Holes.
(c) Dopant atoms.
(d) Valence electrons.
Answer : (c) Dopant atoms.
32. Consider the following types of semiconductors:
1. N type 2. P type 3. Intrinsic 4. Extrinsic
Which of these types of semiconductors are formed by doping germanium with gallium ?
(a) 1 and 3.
(b) 2 and 4.
(c) 1 and 4.
(d) 2and 3.
Answer : (b) 2 and 4.
33. Intrinsic concentration of charge carriers in a semiconductor varies as
(a) T
(b) T2
(c) T3/2
(d) T-1
Answer : (c) T3/2
34. When donor atoms are added to semiconductor, it
(a) increases the energy band gap of the semiconductor.
(b) decreases the energy band gap of the semiconductor.
(c) introduces a new narrow band gap near the conductor band.
(d) introduces a new discrete energy level below the conduction band.
Answer : (d) introduces a new discrete energy level below the conduction band.
35. An intrinsic semiconductor is doped lightly with p-type impurity.
It is found that the conductivity actually decreases till a certain doping level is reached. Why does this occur?
(a) The mobility of holes decreases.
(b) The mobility of both electrons and holes decreases.
(c) The hole density actually reduces.
(d) Effect of reduction in electrons due to increase in holes compensates than the effect of increase in holes on conductivity.
Answer : (b) The mobility of both electrons and holes decreases.
36. The electron and hole concentrations in an intrinsic semiconductor are ni per cm3 at 300 K. Now, if acceptor impurities are introduced with a concentration of NA per cm3 (where NA >> ni) the electron concentration per cm3 at 300 K will be
(a) ni
(b) ni + NA
(c) NA – ni
(d) n2i / NA
Answer : (d) n2i / NA
37. The concentration of minority carriers in an extrinsic semiconductor under equilibrium is
(a) directly proportional to the doping concentration.
(b) inversely proportional to the doping concentration.
(c) directly proportional to the intrinsic concentration.
(d) inversely proportional to the intrinsic concentration.
Answer : (b) inversely proportional to the doping concentration.
38. For a semiconductor, the conductivity is a function of the products of the number of charge carriers and their mobilities. As a result, if the temperature of a slab of intrinsic silicon increases, how does its conductivity vary?
(a) Decreases.
(b) Increases.
(c) Remains unaffected.
(d) Increases or decreases depending upon the rise in temperature.
Answer : (b) Increases.
39. Mobility of charge carrier is given by
(a) v/E.
(b) E/v.
(c) Dn
(d) Dp
Answer : (a) v/E.
40. The conductivity of an intrinsic semiconductor is (symbols have the usual meanings)
(a) generally less than that of a doped semiconductor.
(b) given by σi = eni(μn – μp).
(c) given by σi = eni(μn + μp).
(d) given by σi = ni(μn + μp).
Answer : (c) given by σi = eni(μn + μp).
41. Diffusion current of holes in a semiconductor is proportional to (with p = concentration of holes/unit volume)
(a) dp/dx2.
(b) dp/dx.
(c) dp/dt.
(d) d2p/dx2.
Answer : (b) dp/dx.
42. Einstein’s relation is given by
(a) μ/D = e/kT
(b) μ/D = kT/e
(c) μ/D = k
(d) μ/D = T
Answer : (a) μ/D = e/kT
43. The ratio of the mobility to the diffusion coefficient in a semiconductor has the unit
(a) V-1
(b) cm V-1
(c) V-cm-1
(d) V.s
Answer : (a) V-1
44. A silicon sample A is doped with 1018 atoms/cm3 of Boron. Another sample B of identical dimensions is doped with 1018 atoms/cm3 of phosphorus. The ratio of electron to hole mobility is 3. The ratio of conductivity of the sample A to B is
(a) 3
(b) 1/3
(c) 2/3
(d) 3/2
Answer : (b) 1/3
45. The majority carriers in an n-type semiconductor have an average drift velocity in a direction perpendicular to a uniform magnetic field B. The electric field E induced due to Hall effect acts in the direction
(a) v x B.
(b) B x v.
(c) along v.
(d) opposite to v.
Answer : (b) B x v.
46. A semiconductor specimen of breadth d, width w and carrying current I is placed in a magnetic field B to develop Hall voltage VH in a direction perpendicular to I and B. VH is NOT proportional to:
(a) B.
(b) I.
(c) 1/w.
(d) 1/d.
Answer : (d) 1/d.
47. Which one of the following is the correct statement ? The type of majority charge carriers in a semiconductor can be found by
(a) Hall effect.
(b) Piezoelectric effect.
(c) Photoelectric effect.
(d) Meissner effect.
Answer : (a) Hall effect.
48. Consider the following statements for a p-n junction diode :
1. It is an active component.
2. Depletion layer width decreases with forward biasing.
3. In the reverse biasing case, saturation current increases with increasing temperature.
Which of the statements given above are correct ?
(a) 1, 2 and 3.
(b) 1 and 2 only.
(c) 2 and 3 only.
(d) 1 and 3 only.
Answer : (a) 1, 2 and 3.
49. The depletion layer across a p+– n junction lies
(a) mostly in the p+-region.
(b) mostly in the n-region.
(c) equally in both the p+ and n-regions.
(d) entirely in the p+-region.
Answer : (b) mostly in the n-region.
50. For a germanium P-N junction, the maximum value of barrier potential is
(a) 0.3 V
(b) 0.7 V
(c) 1.3 V
(d) 1.7 V
Answer : (a) 0.3 V
51. When a positive dc voltage is applied to the n-side relative to p-side, a diode is said to be given a
(a) forward bias.
(b) reverse bias.
(c) zero bias.
(d) neutral bias.
Answer : (b) reverse bias.
52. The development of barrier potential in the depletion zone of a PN junction is consequent to
(a) diffusion of majority carriers across junction.
(b) drift of minority carriers across junction.
(c) generation of minority carriers due to thermal energy.
(d) initial flow of conduction current.
Answer : (a) diffusion of majority carriers across junction.
53. In an unbiased P-N junction, the junction current at equilibrium is
(a) due to diffusion of minority carriers only.
(b) due to diffusion of majority carrier only.
(c) zero, because equal and opposite drift and diffusion currents for electrons and holes cross the junction.
(d) zero, because no charges cross the junction.
Answer : (d) zero, because no charges cross the junction.
54. A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10°C, the forward bias voltage across the PN junction
(a) increases by 60 mV.
(b) decreases by 60 mV.
(c) increases by 25 mV.
(d) decreases by 25 mV.
Answer : (d) decreases by 25 mV.
55. Reverse saturation current in a germanium diode is of the order of
(a) 1 nanoampere.
(b) 1 microampere.
(c) 1 mA.
(d) 10 mA.
Answer : (b) 1 microampere.
56. Which of the following is NOT associated with a p-n junction ?
(a) Junction Capacitance.
(b) Charge Storage Capacitance.
(c) Depletion Capacitance.
(d) Channel Length Modulation.
Answer : (d) Channel Length Modulation.
57. Avalanche multiplication
(a) disruption of covalent bonds occurs by collision.
(b) direct rupture bonds.
(c) both (a) and (b).
(d) none of the above.
Answer : (a) disruption of covalent bonds occurs by collision.