Electrical Engineering Materials Multiple Choice Questions and Answers-5 (English)

1. For a particular material the Hall coefficient was found to be zero. The material is
(A) insulator
(B) metal
(C) intrinsic semiconductor
(D) none of the above
Ans: B

2. is an element used in semiconductors whose atoms have three valence electrons.
(A) An acceptor
(B) A donor
(C) Germanium
(D) Silicon
Ans: A

3. The minority carrier concentration is largely a function of
(A) forward biasing voltage
(B) reverse biasing voltage
(C) temperature
(D) the amount of doping
Ans: C

4. For germanium the forbidden energy gap is
(A) 0.15 eV
(B) 0.25 eV
(C) 0.5eV
(D) 0.7eV
Ans: D

5. Which of the following is an advantage of stranded conductor over equivalent single conductor ?
(A) Less liability to kink
(B) Greater flexibility
(C) Less liability to break
(D) All of the above
Ans: D

6. Due to which of the following reasons copper and aluminium are not used for heating elements ?
(A) Both have great tendency for oxidation
(B) Both have low melting point
(C) Very large length of wires will be required
(D) All of the above
Ans: D

7. Copper, even though costly, finds use in the windings of electrical machines because
(A) copper points offer low contact resistance
(B) copper can be easily soldered and welded
(C) copper windings are less bulky and the machines become compact
(D) all of the above
Ans: D

8. Substances whose specific resistance abruptly decreases at very low temperature are called
(A) insulators
(B) conductors
(C) semiconductors
(D) superconductors
Ans: D

9. Which of the following affect greatly the resistivity of electrical conductors ?
(A) Composition
(B) Pressure
(C) Size
(D) Temperature
Ans: A

10. Thermonic emission occurs in
(A) vacuum tubes
(B) copper conductors
(C) ferrite cores
(D) transistors
Ans: A

11. Which of the following materials does not have covalent bonds ?
(A) Organic polymers
(B) Silicon
(C) Metals

(D) transistors
Ans: C

12. The conductivity of a metal is determined by
(A) the electronic concentration and the mobility of the free electrons
(B) the number of valence electrons per atom
(C) either (A) or (b)
(D) none of the above
Ans: A

13. The resistivity of a metal is a function of temperature because
(A) the amplitude of vibration of the atoms varies with temperature
(B) the electron density varies with temperature
(C) the electron gas density varies with temperature

(D) none of the above
Ans: A

14. In a crystal, an atom vibrates at a frequency determined by
(A) the heat content of the crystal
(B) the temperature of the crystal
(C) the stiffness of the bonds it makes with neighbors

(D) none of the above
Ans: C

15. Due to which of the following reasons aluminium does not corrode in atmosphere ?
(A) Aluminium is a noble metal
(B) Atmospheric oxygen can only diffuse very slowly through the oxide layer which is formed on the surface of aluminium
(C) No reaction with oxygen occurs ft Any of the above

(D) none of the above
Ans: B

16. Due to which of the following fact, in India, aluminium is replacing copper ?
(A) Aluminium is more ductile and malleable than copper
(B) Aluminium is available in plenty, cheaper and lighter than copper
(C) Aluminium has lower resistivity than that of copper
(D) Aluminium has less temperature co-efficient than copper
Ans: B

17. The conduction of electricity, in semiconductors, takes place due to movement of
(A) positive ions only
(B) negative ions only
(C) positive and negative ions
(D) electrons and holes
Ans: D

18. ________ has the best damping properties.
(A) Diamond
(B) High speed steel
(C) Mild steel
(D) Cast iron
Ans: D

19. The photo-electric effect occurs only when the incident light has more than a certain critical
(A) intensity
(B) speed
(C) frequency
(D) wave length
Ans: C

20. If the resistance of a conductor does not vary in accordance with Ohm’s law it is known as
(A) non-linear conductor
(B) reverse conductor
(C) bad-conductor
(D) non-conductor
Ans: A

21. Effect of moisture on the insulating materials is to
(A) decrease dielectric constant
(B) decrease dielectric strength
(C) decrease insulation resistance
(D) increase dielectric loss
(E) all of the above
Ans: E